I have the same issue with DIGI. Whenever i switch from WiFi to 3G/Edge, the phone just would not detect back to 3G/Edge network. Airplane mode didnt help much and the only way is to restart the phone and it is able to pick up 3G again.

Not able to isolate if it is the sim or the phone or DIGI issue:(. Will try "reset network settings" later as the phone is not with me now.

Anyone has any solid solution to solve the issue?