I recently updated from 3.8 to 4.0 on my BB 7100t. The phone now drops many calls in the middle, then shuts down. I returned the phone to T-Mo, they sent me a new (not refurb) model, and I upgraded to 4.0 again. GRRR!! Same thing! Talk for 3-4 min... then dropped call PLUS a power-down. It's enraging, and T-Mo's BB support is clueless. They suggested to return to the store and have my SIM card tested, but it was FINE until the upgrade. I'm guessing it's the 4.0.