I also had the same problem like my bb 8900 freezes and call get dropped. If the phone is idle it shows normal screen. Once I receive or make call, within next 3-4 minutes it would give disturbance and then would freeze. Once I plugged it to charger it starts. As per your information I checked my battery and it is bulged on both the sides. I can actually make i spin on table.
has the battery arrived to the end of designed life? if that is the case please let me know from where to get authentic battery.
Any help is appreciated