I did some testing on this and here's my findings:
When in a call, if you put the phone screen near your face it or another surface, it goes blank as expected. This is due to the proximity sensor and not wanting your cheek to accidentally hang up the call or something.
The screen remains unlocked for the duration of the call. The screen WILL go blank when near your face or after sitting still for a bit (10s?), but moving the phone or moving it away from your face will wake it up. After my 1 minute screen timeout, the screen will NOT wake up when you move it, NOR if you touch the screen. You MUST press PWR or VOL UP/DOWN to wake it. Note: Often times I found myself pressing these buttons more than once to wake it. Not sure if its lag or me improperly pressing the button (doubtful). The screen should remain UNLOCKED after waking back up EVEN AFTER the screen timeout period has passed.
After the call, if the screen was unlocked, the phone remains unlocked. If the phone was previously locked, it goes back to its locked state. This is for obvious security reasons (would be bad if an incoming call would unlock the phone).