If you are on Maxis, all current methods - SIM cloning, TurboSIM and even the full hardware Geohot hack does not allow incoming calls. Outgoing calls, SMS in/out, EDGE works just fine. So far, DiGi appears to work the best with all the above methods, Celcom does not work with SIM cloning, but fully functional with the other 2 methods.

If even with the Geohot method Maxis fails with incoming calls, it is most likely a Maxis SIM/network problem, perhaps a bug that prevents the iPhone from fully reading the SIM instructions. Likely then, even with a full software hack, appearing to be imminent from various sources, there would be problems with incoming calls from Maxis.