After I bought the new iPhone I decided to keep the old one as a back up ipod.
I loaded up the leaked copy of 2.0, then erased it and put the official version on it, then wiped it and resynced it. Just because.
I found that even if I had wifi hooked up the phone would not let me reset up the email accounts in airplane mode. I kept getting “Cannot connect using SSL” errors. Turn off airplane mode to set up the email accounts, then you can swap it back to airplane mode on/ wifi on and all will be well.
If you have it in airplane mode it won’t keep searching for the ATT network and run down your battery on you. Plus you won’t keep getting the ‘activation’ error messages.
Don’t worry about wiping it. I totally wiped it and put the 2.0 software update on after I took that phone off the ATT phone plan and had no problems.
You can sync both the old and the new phone with the same computer. You might want to rename one of them. While syncing click on the name of the phone in the iTunes sidebar. It will let you erase the old name and enter a new name.
Purchased music can be loaded on both phones, you are allowed up to 5 devices including the computer where you store all your information.
Remember to reset time zone support [ Settings->Mail, Contacts, Calendar scroll all the way down ] to your time zone. My calendar appointments kept changing times. It drove me nuts for a couple of days till I stumbled upon that setting.
If an activation screen pops up on iTunes while synching your old phone, just select ‘cancel’.