The problem with open mobile phones is neither the phone hardware or software. The main problem is the damn cellular network carriers.
Until some government agency gets serious about forcing the cellular carriers to actually allow phones on their network without having to go through the anal violation that is "certification" for their network, the open mobile phone ecosystem will continue to suck.
It was the governments that require that certification, and for good reasons.
We can play this “wild west hacker” whatever, but rules are a necessity for a working society, one can’t just start driving on the other side of the road, and neither would we be ahead with random frequencies getting emitted everywhere.
Why would the government ever force carriers to accept uncertified devices? So they can emit interference on cellular frequency bands? So they can violate SAR limits and burn people?
The devices would still be subject to FCC certification just like your WiFi chipsets are.
Beyond that, the people developing chipsets generally have better tests for compliance than the carriers, themselves. You should be able to drop one of those chipsets in your phone, plug in a SIM, and get on with life. However, the carriers make you spend a couple of megabucks of bribes and then they will deign to allow your phone on their oh-so-fragile network.
Until some government agency gets serious about forcing the cellular carriers to actually allow phones on their network without having to go through the anal violation that is "certification" for their network, the open mobile phone ecosystem will continue to suck.