The following Princeton University study on Security and Privacy Risks of Number Recycling at Mobile Carriers in the United States details the risks associated with recycling your phone number. You may want or need to relinquish a phone number for a variety of reasons, but it’s important to consider the potential fallout and available alternatives before doing so. A key finding of the Princeton study is that malicious actors can easily discover numbers that have been recycled and then target the previous owners with a variety of attacks. See page 4 of the study for more information on this. Additionally, see page 15 of the study for recommendations on how to mitigate these attack types.
The study recommends that carriers advise customers about the importance of disconnecting a number they plan to relinquish from all associated accounts, including releasing the phone number from all primary and secondary authentication mechanisms, and to consider using a “number parking” service, offered by some carriers. These services can be typically purchased for $2 – $5 per month from services like Numberbarn or Park My Phone. You can also explore Google Voice as an alternative, which allows you to park a phone number for a one time fee, and still receive voicemails and text messages, or forward the parked phone number to a different phone.
Resources:
https://krebsonsecurity.com/2021/05/recycle-your-phone-sure-but-maybe-not-your-number/