1. how do i go about keeping my number and contacts?
When placing the pre-order, you will select as a new AT&T subscriber with an option to have a new phone number assigned, or as porting a number from another carrier. If the latter, you will enter the phone number with area code.
If you are storing contacts on the SIM card, which is limited to a name and a couple of phone numbers and maybe an email address for each contact, the iPhone includes an option to import contacts from a SIM card that was used with another phone. The iPhone does not support storing contacts on the SIM card. The iPhone is designed to be synced with a supported address book application on your computer for contacts via the iTunes sync process. With Vista, this can be with Outlook 2003 or 2007 along with syncing calendar events and notes, or with the address book application used by Windows Mail called Windows Contacts or Windows Address Book.
2. how do we set up a new account on at&t so that my dad and i are on the same contract? he does not plan on getting a new phone.
If he does not plan on getting an iPhone, I recommend placing an iPhone pre-order at a local AT&T corporate store on the 15th. Your Dad will not be able to switch to AT&T until your iPhone is activated which will also port your number from T-Mobile and notify T-Mobile you are canceling your service at the same time. When your pre-order arrives at the AT&T store, you and your Dad can go together to port his number to AT&T at the same time your number is ported to your iPhone and your iPhone is activated with AT&T.