cell phone calls

I just found out that when making and ending a call on my cell, I have to press the red "ending call" button to be disconnected.
However, if I do not press the "ending call" red button the line stays open
for up to 1 to 3 minutes. This means that 1 to 3 minutes is being deducted from my overall minutes plan. Is this clear?
Is my provider siphonning off my minutes? or is this a side effect of using wireless? or not?
If someone calls me and they end the call my line still stays open and minutes are being deducted from my minutes plan. Cumulatively over the course of a month my minutes are being used up at a faster rate than usual. Response is requested. My cell is an Iphone 3gs no os4 upgrade yet.Thanks.

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Thats strange.. as far as i know, as long as one of the party ends the call weather its you are the other person, it should end the count in minutes... How can you tell that you are still being charge for 1-3 minutes even after the call end if you dont press the end button?