What part of the feature set in particular has been lacking in competitors?

EDIT: asking because I've been working on an alternative of sorts. I used GV a lot before I figured I could go without it/Google.

I'm not sure what the OP does, but at least for me I find myself chained to Google Voice for SMS 2FA use because it's basically the only phone number provider that cannot be exploited with a sim swap attack (same deal with Google Fi). And while I don't necessarily trust Google, their account security is leagues ahead of anyone else imo.

I previously looked at jmp.chat but they didn't really inspire confidence on the security front.