what are the circumstances of your call when they drop? are you moving In a car, or are you on foot, lazying on the couch. What type of environment are you in, in your home in a building, did you go hide behind a tree???
Who were you talking to? were they a land line or mobile? if a mobile are you sure it was not their end that dropped the call?
your signal strength can go from full bars to no bars and drop your call in a matter of 1 second depending on where you are at. Then when you look at the phone it shows full bars giving you the impression the phone had full bars all along when it ropped the call. If you have a blue tooth head set you can make sure you have full bars when it drops.
Usually when you have this type of situation in more than one place, the problem will be the phone.
If it only happens in the same 1 or 2 places very consistently it will be a network issue.
there are about a thousand things that will cause your call to drop, so if you can narrow it down a bit that will help you determin what and where your problem is.