Is It Possible to Know the Location of the Caller? If I'm using an Android, is it possible to know the physical  location of the person who call me/ I call to?
Yes. I have not tried the WorldCallPlaceAndTime App but it looks like what you want. Below you can see the summary and screenshot from appbrain. 

EDIT: Based on the comments on appbrain, this app just determines the caller's location based on the phone number's area code. If you want to know the phone's physical location, you'll need to use something like Google Latitude, which does not give you the caller's location during the call (yet).


  This program shows a small
  CUSTOMIZABLE info window during
  incoming/outgoing call: country,
  region, city (or mobile operator) and
  LOCAL TIME in that place (worldwide)!
  
  2.0: colors option for donators, bugfixes
  
  tag: call location,calllocation,who's
  calling,wer ruft an,caller id,who
  called