HTC Tilt 8925 / TyTN II
screen goes blank in call after 10 sec.
http://www.jongma.org/KaiserTweak/ »
You will have a list of NEW options for things on your phone that you can enable and disable. The first one in the list is the "sleep" problem you are talking about. It is pretty handy! Some of the settings require a soft reset to take effect.
It's a PITA to have to constantly turn the screen back on when you're navigating some idiot company's phone menu, but you don't actually have to change anything on your Tilt to do it.