This is often in my workplace. INSERT SIM (1600/1110i/1112/2310) handsets.
Here is the tip before making any attempt to repair the handset via hardware. Believe it or not what I'm about to share to you is 100% cause of insert sim.
Before reheating sim ic, uem, cpu check this first:
OXIDATED CHARGING PIN

Yap, it's true OXIDATED Charging Pin Can Cause "INSERT SIM".
So before anything else....
TITIGAN MUNANG MAIGI ANG CHARGING PIN BAGO BUMANAT... okei?!
Enjoy.