Most modern apps from SaaS to e-commerce collect phone numbers alongside emails during user signup, but unless those numbers are validated with a reliable Phone Validation API, they’re not just useless they can become a serious security risk for your application. In this guide, we’ll break down the dangers of unverified phone numbers, how to stop fake signups and SMS failures, and why tools like Numverify’s phone validation and carrier lookup API are essential for protecting your business.
Table of Contents
Key Takeaways
- Unverified phone numbers can lead to spammy signups, failed OTPs, phishing risks, and geographic spoofing.
- You need a wireless carrier lookup API if your business relies on SMS marketing in any capacity.
- Numverify API is one of the top phone number verification tools that validate phone numbers at the point of entry to ensure they’re real, active, and properly formatted.
- You can block high-risk carriers and flag suspicious phone numbers using Numverify’s telecommunications carrier identification.
- Numverify supports phone validation in 232 countries and works with mobile, landline, VoIP, and business numbers.
- The Numverify carrier lookup API is simple to integrate, secure with 256-bit HTTPS encryption, and returns clean JSON responses.
- Using Numverify leads to reduced fraud rates, better data quality, lower SMS costs, and improved user conversion.
Why Are Unverified Phone Numbers a Risk to Your Business?
Unverified phone numbers can be a serious threat to your application security. To understand how you can tackle them, it’s important to know what these threats may look like. Some of the most prominent threats are:
- Spammy signups and bot attacks
If the entered phone numbers are incorrect, you don’t know if they belong to a human. They can be bots creating fake accounts using disposable numbers. This pollutes your user database with unnecessary data that increases your onboarding, support, and CRM costs. No one wants that. - Failure of SMS & OTP delivery
If a genuine user tries to onboard on your product but enters the wrong number by mistake and if you don’t have a phone number verification system in place, they won’t receive OTPs, or their two-factor authentication efforts will fail. This makes the users’ accounts vulnerable to security threats and paves the way to a frustrating user experience, which, again, no one wants. - Geographic spoofing
When you don’t get the actual phone numbers from users, you also don’t receive their actual geolocation which means it’s easy to fake one’s location. This makes up for misleading data. - Phishing
Even if the entered phone number is correct, validating phone numbers is important to make sure the number belongs to the user who claims it. Without a validation system in place, attackers can impersonate real users.
- Exploratory fraud and data quality issues
Sometimes, users might create multiple fake accounts to unethically avail themselves of referrals and discounts. Moreover, wrong numbers create friction in the SMS or marketing flows that you are paying for.
What Makes Numverify a Top Phone Validation API
There could be multiple ways to deal with spam and fraud in your user database, but the most efficient one is to eradicate it at the point of entry. How, you ask? By using a phone validator API that validates every phone number as it’s entered on your platform, so you know every number in your CRM belongs to a genuine user.
Numverify API is an efficient and accurate phone validator API that helps you make sure that phone numbers in your user database are valid and up-to-date. But why should you pick Numverify API out of the tens and hundreds of APIs out there? Let’s discuss.
- Accurate results
Numverify gives accurate results after validating your phone numbers with data that actually matters to your database. Below is an example response from the Numverify API.
Example Response:
{
"valid": true,
"number": "14158586273",
"local_format": "4158586273",
"international_format": "+14158586273",
"country_prefix": "+1",
"country_code": "US",
"country_name": "United States of America",
"location": "Novato",
"carrier": "AT&T Mobility LLC",
"line_type": "mobile"
}
2. Worldwide support
REST API has support for 232 countries, so you can have users from all across the world and not have to worry about phone number validation at all. Numverify API can check lots of different types of numbers, such as personal phone numbers, business numbers, landline numbers, etc.
3. Simple, secure, and developer-friendly
You can call the Numverify API with just simple HTTP requests and get the results in lightweight JSON format—less fuss and more ease of use. The API is secure, which means your data is encrypted, and HTTPS protects user information during transmission using 256-bit encryption. Developers also pick Numverify API for its clear and concise documentation that keeps a log of all of its features, small and big.
4. Advanced tools
Along with verifying your user phone numbers, Numverify gives you a look into deeper metadata about which carrier the number belongs to, whether the number is mobile, landline, or VoIP, the location it belongs to, and more. This phone carrier lookup​ API also checks if the numbers match the current numbering plans that change over time. This helps you detect fraud and perform precise analytics on your data.
5. Usage statistics
With Numverify, you can get a real-time picture of how many API requests you’re using. You can get daily or monthly API usage statistics and receive notifications when you are close to your limit, so you can simply upgrade or limit your usage so as not to cause disruptions in your app or service.
6. Gentle on your pocket
You don’t need to break the bank to use this one. Numverify has a generous fee tier plan that offers 100 phone numbers per month—perfect for devs or small teams just getting started with phone number verification. You can go for higher-tier plans that start with just $19.99/month.
How Numverify Validates Numbers and Detects Fraud (And What Data It Gives You)
Numverify API is a strong and reliable bulk phone number validation solution for businesses of all sizes that collect phone numbers from their users. As soon as a phone number is submitted, Numverify cross-references it against its perpetually updated international numbering plans. This ensures that the number is accurate, working, and correctly formatted. The phone validator API gives you information like:
- Validity: to indicate if the number is active and can be reached via channels like SMS
- Format: provides a standard representation of the number to see if it is local or international
- Country: this includes the country name and code of the number holder
- Location: a more specific location like the city or region associated with the phone number holder
- Carrier: to identify the mobile service provider associated with the number
- Line Type: specifies if the number is mobile, landing, or VoIP
Using the carrier and line type data that suggests the service provider and line type, Numverify works to identify if the numbers have been or are involved in fraudulent activities. VoIP numbers, for instance, are often associated with online services and can be used by someone to hide their identity. Or, if there is a carrier mismatch between the information provided by the user and the numbering plans, it may indicate a risk of spoofing.
Using Numverify not only gives you comprehensive information about all your numbers but also helps you detect spam and fraud long before it gets to a bothersome point.
Why Carrier Lookup Matters for SMS & Fraud Protection
If you’re still debating whether or not you need carrier data of your users, the short answer is yes, you do. Not only is it challenging, but it is almost impossible to grow an application that requires sign-up verification without cell phone carrier identification if you intend to maintain a successful SMS marketing flow.
Basic phone number validation tells you whether the numbers are formatted correctly or are reachable. Most of the time, that’s not enough. Just because a number is active and reachable doesn’t mean it will receive the message you are sending or that it will be relevant. Carrier data helps you determine who the user is, how they are connecting with you, and whether or not their number can be a security threat.
A carrier lookup API helps you determine whether a number is mobile, landline, or VoIP, so you can filter out and send messages to only the number to numbers that are relevant. Moreover, the knowledge of carrier data of your users’ phone numbers enables you to personalize the contents of your message depending on their location. Each telecom provider can have their own slightly different regional messaging regulations that you can comply with only when you know the carrier data of these numbers. So, there seems to be hardly any reason you shouldn’t focus on enhancing SMS delivery with carrier lookup.
Numverify returns carrier data as a result of your API requests. This carrier data identifies the telecom provider associated with phone numbers and helps you prevent fraud.
1. VoIP number detection
VoIP stands for Voice over Internet Protocol, and this can be used to make phone calls over the Internet without using actual phone numbers. Numverify can check for line type and block/flag VoIP numbers. Here’s what this looks like in Python.
if data['line_type'] == 'voip':
print("Flagged: VoIP number detected.")
# Trigger CAPTCHA or block account creation
2. Carrier mismatch alerts
Your API number lookup system also checks for carrier mismatch. If, for instance, the user is from India, but their phone number is from a US carrier, that’s something to be flagged. This can be cross-checked with IP addresses, billing info, or app location.
expected_country_code = 'IN'
if data['country_code'] != expected_country_code:
print("Suspicious: Carrier country mismatch.")
# Alert system or ask for re-verification
3. Blocking known high-risk carriers
Some carriers are popularly known for being abused for spammy and fraudulent activities. Simply maintaining a list of such carriers and flagging them would ensure app security.
high_risk_carriers = ['Google Voice', 'TextNow', 'FreedomPop']
if data['carrier'] in high_risk_carriers:
print("Blocked: High-risk carrier.")
# Deny signup or flag for manual review
How to Use Phone Number Validation in Signup, Checkout, and CRM Flows
- Signup flow
You can validate numbers as soon as the user enters the phone number while creating their account on your application. If the number and mobile line are valid, the user can go ahead with an OTP-based verification and create their account. If not, it can show an error and prevent them from submitting the form. - Two-factor authentication
Your phone carrier lookup​ API can also validate the number just before sending the OTP. This way, the OTP gets sent only when the number is valid, preventing fraudsters from using disposable numbers to get into your application. - Checkout
If you have an E-commerce business, it also makes sense for you to validate your users’ phone numbers during or right after the user provides their phone number at checkout. This ensures that users’ phone numbers are validated before processing the order and avoids failed deliveries. - CRM cleanup
If you have a contact list in your CRM that hasn’t been seen or worked on for a while, it probably needs a cleanup. Look through your stored phone numbers and check if all of them are still valid and active, then remove the ones that are not.
Here are some best practices you can follow to use your phone validator API the best way:
- Validate as soon in the workflow as you can to eliminate any spam and frauds early on.
- Use location metadata to automatically detect and auto-fill country code dropdowns and even personalize messages or language if you want. This also gives you a chance to check if the rest of the data, such as the IP address, matches the location.
- Add on top more security layers like IP intelligence, email validation, device fingerprinting, and CAPTCHA, to really foolproof your application.
- Depending on the line type of the number, make it go through different review processes. For instance, allow only mobile numbers for OTPs, flag VoIP numbers for extra review, and log landline numbers for audit.
- Monitor your daily or monthly phone number carrier lookup API usage to make sure you are not exceeding limits.
Proving the ROI of Phone Number Validation
The intention of using a phone validator API is not just to detect fraud and improve security. It is also supposed to bring in measurable business impact across the board. These metrics should help quantify cost savings, revenue impact, and operational efficiency across your organization. Here are the metrics you can check for in your organization to measure if your phone carrier lookup​ API is bringing in the results you want it to.
- Reduced fraud rates
The direct consequence of using a carrier lookup API is a reduced number of frauds. This means fewer fake signups and bot accounts on your platform, decreased use of multiple accounts to gain repeated referrals, and reduced custom support costs. - Improved conversion rates
Using a reverse phone lookup API results in higher success rates in OTP and 2FA, making the onboarding process smoother and thus also impacting conversion rates. There are fewer form abandonments because phone numbers get validated in real-time, and your SMS-based marketing updates actually reach your users. - Better data quality
Using the Numverify API makes sure you get access to accurate user profiles and data, which means streamlined CRM flows, clean datasets, and reduced data cleansing costs. - Cost savings in communications
Detecting invalid phone numbers leads to a much lesser SMS bounce rate and provider charges. This means your transactional alerts are more reliable and reach the right people. - Developer and Ops efficiency
Using a third-party phone validator API takes away the fuss of spending time on building in-house validation rules. When you have one less thing to worry about, you can focus more on actually building the product.
Final Thoughts: Why Phone Validation Should Be Part of Every User Flow
Using a phone validator API is not just an add-on feature, but a crucial business need for all teams across the world. No matter where you are in the world, if you have real users, you need phone number validation in your workflow.
👉 Start using Numverify for free — includes 100 monthly api requests, no credit card required.
👉 Learn how to integrate Numverify into your app in minutes.
Frequently Asked Questions
- What is a phone number validation API?
A phone validation API checks if a phone number is real, active, and correctly formatted. Tools like Numverify also identify the carrier, location, and line type (mobile, landline, VoIP). - Why is carrier lookup important for businesses?
Carrier data helps detect VoIP numbers (often used for fraud), filter out landlines in OTP flows, and personalize messages for regional compliance. The biggest use case for applications is validating users during the signup process. - Can Numverify detect VoIP or fake numbers?
Yes, Numverify’s line_type field flags VoIP, landline, or mobile numbers. You can block disposable or suspicious numbers in real time. - Is Numverify free to use?
Yes, Numverify offers a free tier with 100 monthly requests. Perfect for start-up application and testing. Paid plans start at $9.99/month with more requests and standard support. - How does phone number validation reduce fraud?
It stops bots and spammers at the entry point by blocking fake numbers, ensures OTP delivery to real users, and reduces costs from SMS bounces or fake accounts. - How do I integrate phone number validation API into my app?
You need to integrate a phone number validation api From there, you send a simple HTTP GET request with your API key and the phone number. You should get a response with JSON containing validation, carrier, and location details.
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