How much would it all cost to get a new 3gs, and cancel the att contract but still keep the phone?
To buy a new iPhone 3GS without contract is $699. If you mean that you want to buy it, keep it for a month, cancel service, and pay the termination charge, then that would be:
$299 for 32 GB iPhone 3GS
$36 activation
$82 for 31 days of service
$170 early termination fee
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$587