Unusual dialog box requests restart

[bussoboy]

Model # GT-I9300, Android version 4.1.2 Baseland I 9300xxEMAS Kernel 3.0.31-1287119

Hi, my little phone has been working very well for many years but today, a dialog box appeared which stated:
SIM CARD REMOVED.
Mobile network will be unavailable
until you restart with a valid sim card
inserted.

When I press "RESTARD" the phone shuts down and restarts normally. After that it operates normally for several hours or days when the same box appears and the sequence is repeated/

 

[mikedt]

Your SIM card could be faulty? Try getting a replacement from your carrier. Friend of mine had the same thing happening earlier this year, and the carrier replaced the SIM with a new one.

 

[Dannydet]

https://en.m.wikipedia.org/wiki/Samsung_Galaxy_S_III
I'd opt for a new phone at this stage