although I don't have one, I know people have reported that the Diamond (and Touch Pro) have issues with the touch screen being accesible when a call is being received.
So if the device is in your pocket and you receive a call, you could accidently activate the touch screen or reject the call.
There is an application available (actually there are quite a few where developers rose to the challenge) to lock the touchscreen, but still allow you to use the accept/reject call softkeys.
One of the applications is listed here:
[APP][17.09.08] Answerkeys Disabler (v0.3.1) - xda-developers