Im using VF simcard on Telecom Galaxy S I9000T
theres nothing wrong with using this phone except for the fact that 3G is not working and sometimes phone call is hung up itself i think its because of network disconnection

Plus
it shows this error message saying
Sorry!
The process com.android.phone has stopped unexpectedly.
Please try again.
Fore to close

then network disconnects for like 5~10secs
and then it turns on again itself

what does this mean?
how can i fix it?