I don't get why people think there is so much conflicting information. There is but all wrong.....
1) yes the sim comes set up for the line you upgraded.
2) AT&T can reformat the sim with the SIM card number and attach it to the imei of that phone.
3) so on power up the phone connected to the network and sees it needs to update........
The steps are
1) call AT&T with the imei and SIM card number
2) press 2 for upgrading but switch the lines
3) tell rep and they are care of it....
here is my backup!
http://www.att.com/esupport/article.jsp?sid=KB411462#fbid=H8VMnfGIoLl
YOU DO NOT NEED A NEW SIM!!! and this is from a order from apple.com. Just a FYI. and I still do not need a new SIM...
This is for AT&T.. Figured I would add that. Same goes for Verizon though....
----------
Please read my last post...l. Why do yo u need a nano sim...