Fair question. I certainly don’t have any limits on the SIM that I’m aware of, I’ve used it for years, and it’s normally a dual sim in my main phone, and can make calls data text etc without restriction. so, I would be a bit surprised if putting it in a different phone caused limits to be imposed!
Yeah, it was my main SIM for years, and then I moved country, and I kept it as a second SIM in a dual sim phone since then, but I have never stopped using it. It’s been in Android and iPhone phones too. No issues thus far.
And I believe if the SIM was being locked by the carrier it would not work for anything.
This means that VoLTE is not operational; otherwise it would remain on 4G/LTE during the call.
Do you have the BM818 Tool installed, with VoLTE enabled?
If you already have it enabled and calls are still dropping to 2G, then either your carrier isn’t implementing VoLTE on their network (or the foreign network isn’t doing so for the BT SIM*), or the carrier isn’t implementing VoLTE for the L5 (actually the BM818 modem, which is in common use in the automobile industry).
*Since you’ve used the SIM successfully in other phones, you can probably rule that out.
Maybe ask the carrier whether customers are supposed to be using VoLTE.
If you know someone else using that same carrier, maybe check on their phone. (On an iPhone, for example, if the carrier has made VoLTE mandatory then the VoLTE setting simply disappears, otherwise there should be a setting for it that you can check.)
I’m in the US and my outgoing calls are doing the same dropping off and not going through. Incoming calls work fine. I have a local cell carrier that has Verizon as a partner and the phone defaults to Verizon. My local carrier still uses 2g calling, but upgraded their SIMS for VoLTE.
Everything else works. Data didn’t work at first and did after I added my carrier’s APN.