I once had the same problem. This worked for me: [UNOFFICIAL BUILD] Sony Xperia XZ1 Compact (lilac) e-1.3-q Post #212 - #210 by Taurus
If you don’t have an XMPP account loaded, you might try SIP instead. If neither, just try: power down, remove the SIM card, power up, attempt to use the dialer (won’t go anywhere, of course), power down, reinsert SIM, power up. Then check functionality.
You might also try doing a temporary test/switch with a different SIM, if you have one lying around, even if it’s an inactive SIM.