It's bizarre you're experiencing that. I always thought the Galaxy S had some kind of motion sensor that sensed when you moved the phone away from your ear to hang up or use the keypad etc.

 

I'm experiencing the same problem, I'll keep on searching for a fix or hack. So if anyone that know how to change some kind of secret settings, please chime in.

 

I am having sort of the same issue with my galaxy s2, not when entering numbers but when I make a call a lot of times i need to hit extensions or even just to hang up I have to power up the screen again, why would it timeout in the first few seconds while you are making a call? seems like a stupid feature

 

I’m having the same issues and it’s obvious we’re not alone. Doesn’t anyone have an answer to this?...

 

Try this!

http://www.appbrain.com/app/keepscreen-(now-free)/com.tni.KeepScreenLite