Gophone prepaid micro SIM options for iPhone 4?

Hello,

I have a European (factory unlocked) iPhone 4 (similar to those on AT&T although unlocked). I am coming next week to San Francisco, CA for a two weeks stay and I would like to use my iPhone 4 for voice and data (prefrably on a prepaid plan). So my questions are...

1. Can I go to an AT&T retail store and ask for a Gophone microSIM for iPhone 4? Do they give micro SIM cards for prepaid? Should I just ask for a normal SIM and use a microSIM cutter?

2. What is the cost of the SIM card? Do they give it for free if I add a certain amount of funds to my account?

3. If I use the $2 Unlimited Daily Talk and Text plan what is the the biggest data feature package that I can add in my account?

4. Is there an addon package thatn can reduce the international long distance rates to Europe (currently $0.49)?

Thanks

Pavlos