Fraudulent signups cost businesses millions each year in wasted marketing spend, skewed analytics, and increased support costs. While CAPTCHAs and email verification help, one of the most effective tools for fighting fake signups is phone number validation.
By checking the authenticity and risk level of a number in real time, you can flag suspicious activity before it enters your system.
In this article, we’ll explore how phone validation works as a fraud prevention tool and how your business can use it to keep fake users out and good users flowing in.
⚠️ Why Fraudsters Use Phone Numbers
Fraudsters often rely on bulk-created VoIP numbers or recycled mobile numbers to:
- Create fake accounts for coupon abuse or affiliate fraud
- Inflate user acquisition metrics
- Trigger referral rewards
- Attempt brute-force attacks or test stolen credentials
- Bypass duplicate checks on forms
Without validation, your systems may treat these as legitimate users. But under the hood, many of these numbers share telltale signs: wrong format, high-risk carrier, suspended status, or a recently ported identity.
🧪 What Phone Validation Checks
Modern phone validation APIs like CheckThatPhone go far beyond just checking if a number “exists.” Here’s what they look for:
- Line type – Is it mobile, VoIP, or landline? VoIP is often used for abuse.
- Carrier name and subtype – Known high-risk carriers can be flagged.
- Deactivation status – Suspended or recycled numbers indicate risk.
- Porting history – Recent porting may suggest spoofing or SIM swaps.
- Deliverability – If the number can’t receive a message, it’s likely fake.
- GeoIP vs. phone mismatch – If the user IP is in Canada but the number is a U.S. landline, that may signal suspicious behavior.
All of these signals help you determine whether to allow, block, or challenge a signup.
🧰 How Businesses Use It in Practice
1. Signup Form Filters
Validate the number in real time and show an error for invalid or high-risk entries. Bonus: it also catches typos and increases conversion quality.
2. Shadow Risk Scoring
Use the API to assign a fraud risk score behind the scenes. Route suspicious signups to manual review or challenge flows.
3. Duplicate Prevention
Flag when multiple accounts use the same number (or VoIP ranges known to support mass signups).
4. OTP Gatekeeping
Ensure one-time passwords only go to reachable, mobile devices — not burner phones or landlines.
💡 Bonus Tip: Combine with GeoIP
If you collect the user’s IP address at signup, CheckThatPhone can compare that location to the phone number’s expected region. If there’s a mismatch — for example, a VoIP U.S. number submitted from a foreign VPN — you may want to verify further.
This added context is especially useful for:
- Financial platforms
- Lead generation companies
- E-commerce
- Online communities or forums
- Subscription-based SaaS apps
✅ Final Thoughts
Phone number validation is one of the simplest and most effective ways to reduce fraud at the source. Instead of waiting for bad behavior to surface, you can block risky users before they enter your system.
CheckThatPhone provides real-time validation for U.S. and Canadian numbers with insights that help you:
- Detect VoIP abuse
- Flag recycled or suspended numbers
- Identify mismatches and anomalies
- Protect your funnel and your data
👉 Start your free trial and make phone intelligence part of your fraud stack.