Mobile service disconnected

[AKAK]

Cannot make calls.  Brand new phone,  bought in Thailand.  Worked fine in Thailand. Changed to Cambodian Sim,  now I can't make calls. . There is a little X above the service bars icon at the top.  Settings say "mobile service disconnected" 

Thanks 

[CameronT]

Hi @AKAK, welcome to the community.

Is your phone network locked? You can dial *#*#7378423#*#* then go to Service Info > Sim Lock to check.