I have run into folk that alter the phone a bit too much. That is, they will put in task killer apps and then complain.

After they have complained for a few months I find they allow the cell carrier to do a full hard reset back to the carrier's installed load and apps. If there is nothing wrong with the phone, it works fine.

But then again, there are folk that can't resist tinkering or killing apps they don't want.
Bob