I’m facing quite a conundrum here, and if you could help me sort this out, it would be great.
So here are the facts: FP2 (bought summer 2016) cannot receive a call, and hardly manage to make one (bad audio), but it can receive text messages and send them. The call may work from time to time (at a frequency of 1 call in 3 days).
What we have tried:
Unmount and remount the phone, remove dust (not much), tighten other screws : problem remains.
put the sim card to another (working) FP2 (bought June 2017): no problem.
put the sim card of the working FP2 to the problematic FP2: no problem.
look at the service provider’s closest antenna to see whether there was an issue there (no issue)
So it appears that both the FP2 and the sim card are functional independently, but not together.
Edit : We’re in France, with Bouygues Telecom as the service provider.
How is that possible ? Where is the glitch ? Or, better, what can we do ?
How about the signal strength? Have you tried everything you mention at the same location or did you do your trials in different places? Are the two SIM cards from the same provider or is there a chance that the SIM of the other phone makes your phone connect to a closer base station from a different provider?
If the antenna is broken it might be just enough to connect your phone to the base station but not enough for doing a call. Text messages however use the signalling channel.
Do you use mobile data services with your phone? If yes, can you access websites etc.?
So I’d propose: Get closer to a base station and try again or otherwise (if mobile data doesn’t work, either) search the forum for antenna issues.
As for the mobile data services, I do have them activated (4G) and I can go to the internet. When trying to call, the signal goes from 4G to H, the call fails, and it comes back to 4G.
What I meant was that SMS doesn’t really need much signal strength, it works on a very low level.
You could limit your SIM card to 3G to check whether mobile data still works when it uses the same radio access technology as the call.
Settings → Network & Internet → Mobile Network → Preferred Network Type (translated from my German Lineage OS)
If not then this could be an indicator for bad reception. And you could limit the SIM to 2G to see if calling works via this radio access technology (if your provider didn’t cancel this service yet). This would indicate that something is odd with 3G in your phone, at your place or at the base station.