Originally Posted by vmladenov
Why would you unlock an 8310 to use it on T-Mobile the 8320 is way better
This post does nothing to answer the OP's question, and which device is better is a matter of want/need/preference.
As to answer the question, since you don't have AT&T service, I don't it will be covered under warranty through them. I am sure someone will correct me if I am wrong on this.
Have you tried swapping trackballs with your wife's curve just to see the issue is the trackball and not the device itself?