Yes, as long as your with the same service provider. It also has free Wi-fi. Unlike the "Blackberry" you can just put in your old Sim card and it should work just as well.
The iphone 4 comes with a micro sim. Your normal sim will not work with it. My AT&T dealer says he can transfer data directly from your sim/old phone to your new iphone 4.
No!
Yes it can be swapped. I actually swapped my razr's sim card to my iphone. Nothing happened. It works perfectly.
No
If your 3GS is locked, you can't insert a SIM card.
CAN YOU PLEASE HELP ME OUT HERE..
any AT&T phone that can take that sort of sim card.
Put the SIM card from the new phone into the old one. Copy the contacts from the old phone's memory to the SIM card. Put the SIM car back in the new phone - then - either copy the contacts to the new phone's memory - or leave them on the SIM card. Either way - the new phone will find them.
You put a sim card in it.
Yes, Yes you can.
No reason why not - the old SIM card should still work.
Verizon doesn't have sim cards. Only AT&T.