I have a Samsung S3 which normally behaves itself. Recently I've been intermittently getting "Not registered on network" when trying to make calls. Usually happens when I'm at home. I've got a good strong mobile signal.

I've googled the problem and the answers mainly talk about corrupted IMEI which is not the case here. My IMEI is showing correctly.

Any thoughts?

Just a thought -
I had a problem, as it happens also with a S3, with a "worn out" SIM, which intermittently caused the phone not to be recognised on the network.
Your provider will be able to send a replacement. Could be worth trying.
The SIM could also be loose in the fitting.

Thanks for the insight. I had already pulled out the SIM and cleaned the contacts. Seems to be fitting tightly in its socket. I'll do it again with a squirt of Servisol (edit: Tried this and didn't help). I also removed the battery and left it out for a minute or so.

Yep. Same here. No obvious problem.

A replacement SIM did the job for me. Can say no more.

Went into a 3 store this afternoon. They went through various test and tried a new SIM. Phone itself is in trouble. Tomorrow morning I'll go up to my local phone fixers. If they can fix it all well and good, otherwise I've been contemplating getting a Samsung S8.