Incoming calls end after 2 mins 5 secs

I've read about a similar issue on Vodafone some time ago, although in that case it was after 29 minutes and 50 seconds. Still, I think it could be the same issue and it's just that different networks set different timeouts.

The issue seems to be that on 4G calls (and I think WiFi calls) the network requires the handset to periodically send in a keep-alive message during the call, to let the network know that the call is still active. And some Android handsets send the keep-alive signal in a format the network equipment doesn't recognise.

So I'm guessing Three's/Smarty's network tells the handset to send the keep-alive message every 2 minutes. Your handsets are probably doing this, but in a format the network doesn't recognise. So after waiting a few seconds' grace period, the network decides it hasn't received a valid keep-alive message, so the call must be over.

I believe this is why Smarty has a list of devices which are not compatible with its 4G calling here. The two Motorola devices you have tested are not listed, but maybe Smarty's list isn't comprehensive.

Here's a discussion on Reddit which goes into technical detail about the issue which was occurring on Vodafone.