It just makes many services such as Credit Karma unavailable to anyone but the first person to signup.
https://www.fcc.gov/general/wireless-local-number-portabilit...
Is it possible to "park" your phone number until you can start a new plan?
Though AFAIK there's no law or contract term preventing Google from starting to charge a monthly fee in the future.
And after some time — for me it was 5+ years, porting from a baby Bell land line to a postpaid T-Mobile family plan for a couple years and then to Google Voice — your number will be tarred and feathered as a "VoIP" number and rejected for identity verification by some parties until it's ported back to a paid service (again, after some time).
Even so, it's nice that Google lets me keep the number I was born with for $0/month for as long as it lasts.
This is despite written emails from their support confirming the use case (videography) and storage needs were suitable, and a written statement that she is "permanently grandfathered" once Google stopped offering the plan to new customers.
To make matters worse, they gave her 30 days to download all data before everything would be deleted permanently. This is how Google treats "enterprise" customers.
Where things get fun is when Google Voice IS your paid service (e.g. google fiber's phone service, popular with a certain demographic that used POTS for most their life and want to continue having a similarly behaving service).
They're not tied to your person with much more permanency than a DHCP IP address. There's no process to verify your identity or recover your number or help you regain your accounts. The actual process for migrating your number is "Sign up with this other brand you've never tried before and tell them to politely ask your former brand to release the number to them".
If I lose my phone to a trash compactor, the process to change anything in my phone carrier account with regard to SIM cards is going to forward things to my Gmail account, which at random times for random reasons is going to begin to demand 2 factor identification for logging in on a new device via texting my phone number.
There are all sorts of crazy scenarios that can arise with double binds like this.
If we had a resilient authoritative identity verification (say, the DMV, or US Passport Office), or if we had a diverse variety of low-trust identity factors that we could check multiple aspects of ("text my mother" / "Here's a bill showing my address" / "here's a video of my phase saying my phone number"), there would be a way out, but all of corporate America heard "2fa is required for security now" and said "So we just text them right?"
That makes your phone not "another thing that people can use to talk to you in circumstances when you're not accessible", which the FCC's portability plan was maybe sufficient for, but a fragile single point of failure for your entire identity.
Unlike in Germany, where you can’t get one without a passport or ID card.