Fergal Parkinson
Published on: March 7, 2025
The concept of mobile phone number recycling may seem strange but is essential. Mobile phone numbers aren’t endless, and the demand for them is constantly rising. But what happens when a number is recycled? And what are the potential security risks for businesses relying on phone numbers for customer identity verification?
Mobile phone number recycling is the process of reassigning a previously used number to a new customer. When a number is deactivated by its original user, it doesn’t stay inactive forever. After a specified period, mobile network operators (MNOs) can repurpose it for a new user. This recycling process helps MNOs manage the limited pool of available phone numbers effectively, especially as the number of mobile users continues to grow.
When a phone number is recycled, it shifts identity from the previous owner to a new one. However, while the number itself is reassigned, remnants of the previous owner’s digital footprint can still be linked to it. That means the new owner may receive communications, notifications, or even attempts to access services meant for the previous user. This phenomenon, where data linked to a phone number doesn’t immediately update with its new owner, presents potential risks in security and privacy, impacting businesses that rely on these numbers for customer verification and fraud prevention.
Every MNO has a unique approach to recycling, typically involving three stages:
Deactivation: When a user stops using a mobile number (perhaps because they’ve switched providers or upgraded devices) the MNO deactivates the number after a certain period. This deactivation also applies when accounts remain dormant without payment.
Dormancy Period: Once deactivated, numbers are usually held for a set dormancy period to ensure the previous user doesn’t reactivate it. In the UK, dormancy periods may range from 30 to 90 days, depending on the carrier. This buffer is intended to minimise immediate reassignment but isn’t always enough to clear the number’s history fully.
Reassignment: After the dormancy period, the number becomes eligible for reassignment. While MNOs may reset or erase data associated with the number, data remnants sometimes remain connected to online services, especially in systems relying on SMS-based two-factor authentication (2FA).
The phone number recycling process varies globally, with some countries operating shorter dormancy periods, which can further amplify security risks associated with reassignment.
Privacy Concerns: Recycled numbers can create privacy issues, as the new owner may receive messages, calls, or notifications meant for the former owner. This situation can lead to unintended data exposure, affecting both individuals and businesses.
Access to Online Accounts: There are two things that can happen in regards to accessing online accounts. Firstly, the new owner might get access to or information belonging to the old owner simply by entering their number. This was very common on WhatsApp where there were no other checks than the number, so someone would automatically be logged into an account that wasn’t their own. The second is that new users may be prevented from creating an account at all, because their number is associated with an old account that has not been updated. One number cannot be associated with two accounts on the same platform at the same time.
Identity Confusion: Businesses that rely on phone numbers for customer contact or verification may experience issues if a number has been reassigned. For example in countries with advanced privacy laws (such as GDPR) organisations can incur the wrath of data subjects by sending communications that, from the new owners’ perspective, are unsolicited.
Yes, mobile phone number recycling is a genuine fraud risk, particularly for businesses reliant on phone numbers for secure user identification and verification. Here’s how:
Increased Potential for SIM-Swap Attacks: There have been cases of people deliberately taking over a number that belonged to a target to commit fraud, but this has normally involved some kind of insider fraud where an employee of the operator is also involved. This may sound rare, but it is a growing problem for operators in several countries.
A number recycle is by definition a SIM Swap since the new owner will not have the same SIM card as the old owner. After this swap, the number is now perceived to be more ‘risky’ which can affect the ability of the new owner to apply for new accounts and carry out transactions.
Impact on Businesses: From financial institutions to social media companies, businesses relying on phone numbers for verification risk exposing themselves to fraud if numbers are recycled. This can lead to customer dissatisfaction, a breakdown in trust, and even financial losses or failure to comply with industry legislation.
Businesses need to stay aware of these risks, particularly as fraudsters exploit vulnerabilities related to phone number recycling.
MNOs worldwide have varying recycling policies, affecting the timeline and approach to reassigning numbers:
Variations by Carrier: UK MNOs such as EE, Vodafone, and O2 typically enforce a dormancy period between 30 to 90 days. While these policies aim to reduce issues with recycling, they don’t eliminate the risks entirely.
International Differences: In some countries, dormancy periods are shorter due to high demand for numbers, increasing the likelihood of residual account access. This makes it essential for businesses operating globally to be vigilant in managing recycled numbers.
Suggested Best Practices for Carriers: Extended dormancy periods, stricter data-clearing protocols, and alert systems that notify businesses and users about potential recycling issues could all help mitigate these risks. However, MNOs need to balance number availability with security concerns.
As a leader in mobile number intelligence, we offer solutions to help businesses manage the complexities and risks of recycled numbers.
As the demand for mobile numbers increases, the recycling of numbers is here to stay. However, the security risks associated with recycled numbers, from accidental data leaks to fraud vulnerabilities, are significant for businesses relying on phone numbers for customer verification. To stay ahead, companies must adopt intelligent mobile number verification solutions ensuring they’re protected against the hidden risks of recycled numbers.
For businesses and individuals alike, the advice is clear: stay vigilant, update contact information promptly, and use advanced verification methods whenever possible. In a world where digital identity is increasingly mobile-centric, awareness of phone recycling risks is essential for maintaining both privacy and security.
To learn more about how TMT ID can protect your business from the risks of recycled numbers, explore our mobile intelligence solutions or contact us for a consultation.
Last updated on March 7, 2025
Did you know, you can check if numbers have been recycled? We offer an API to check the status of a mobile number, and how long ago the most recent recycle happened.
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