It's never a good idea to rely on one number, or one email address, etc... The day you lose this you lose all your connections.

While one might lose their email losing a phone number is way way harder.

I'm not sure how it works in US but in Finland you have guaranteed transferring across operators. Guaranteed as in fines will tick if the operator from which the number is transferred away is having some 'problems'. Not surprisingly those kind of problems are almost nonexistent.

A last ditch fix would be to get a new phone number and port your old problem phone number to a VoIP service with an Android app