Why does phone keep switching off? I have an HTC Desire Z which I have bought 3 months ago and I usually use it for phone calls. I don't have many apps in it. Sometimes when I call from my phone it switches off and then I have to remove and reinsert the battery to restart it.
What could be going wrong here? I have Android version 2.2 on my phone.
Hacker solution: Root it and flash a new kernel. 

Mainstream consumer solution: Restore to factory settings and see if that helps, or go to your wireless carrier store and have them flash your phone.