Will the ATT store transfer old phone #'s & info?
If you are an existing AT&T subscriber, the iPhone will be activated with your AT&T line/number. If you are a subscriber with another carrier, AT&T will handle the porting of your number for the other carrier to AT&T and the iPhone. AT&T is in the cell phone business - they have been activating cell phones much longer than Apple stores.
What other info are you referring to? If contact info stored on the SIM card which is limited to a name and a couple of phone numbers, the iPhone includes an option to import contact info stored on a SIM card. The iPhone does not support storing ANY data on the SIM card. The iPhone is designed to be synced with a supported application on your computer for contact info which can include much more data than a name and a couple of phone numbers.
Contact a local AT&T corporate store to see if they have the iPhone you want in stock - the 3G or 3GS with the storage capacity you want. If so, you can do everything at the AT&T store with both iPhones activated before leaving the store, and the sales price is identical regardless where an iPhone is purchased.
Also Steve announced the new OS4 for iPhone. Will this be an upgrade to the current hardware or a new hardware release?
OS4 is a firmware update for the iPhone, which is free to all iPhone users with an iPhone that is activated.