Iphone 4/4s with Straight Talk?

I'm really confused with this and I would like to know!
I've been reading about Straight Talk and their $45 Unlimited monthly plan. I've also read about how you can now use AT&T based phones and T-mobile phones.

My question is, if I buy an Iphone 4/4s from AT&T, can I use it with a Micro SD sim from Straight Talk? If so, how do I activate it? Can I just activate it like I would any other Iphone?

I would also like to know how exactly it would work, if it does. (The plan that is, with the phone.)

ANY information on ST would be very helpful, especially with the use of Iphones.
(Does it get good coverage? How does the internet/data plan work? Can I still send MMS? Will I be able to use all the features just as I would with a normal Iphone plan?)

Sorry it's a lot, but I just want to be positive on this! Thank you. Any help is very much appreciated!

Added (1). Also, one more question: If MMS doesn't work until you get iMessage or whatever, can you still like upload pictures via facebook or the internet?

I have an iPhone 4, with straight talk. And they definitely hide a few things. You have to go on safari, find the APN website, download it, and have an app on your phone in order to get Internet. And, you can't send pictures unless you do it through iMessage. When you order the micro sim, the explain how to set up your phone. (VERY easy.) Service is the same as AT&T because Straight Talk uses AT&T towers.At&T phones work great. I LOVE having unlimited everything. MMS isn't a big deal for me. I use text now if I can't send a picture through iMessage. You have to order your micro sim from straighttalk.com for 15$.

Autumn something is wrong with your iphone, i use my 5 and my brother uses his 4s, everything works, mms, sms, data all work and didn't need to install anything