using ipad abroad confusion

I'm planning on travelling to the states in a month or so and am really confused with my options of getting my ipad connected to the net. Firstly I have a uk wifi only model. For when I out and about I use my unlocked mifi device with the ipad to access the net. I was planning on purchasing a at&t gophone pay n go sim, adding the data bundle and using that in the mifi. But after some research I found that I may need a phone with the gophone sim in to activate the sim online? I assumed the sim could be activated online and that's it, the I would just have to add at&t's apn settings to the mifi and every thing would work. I'm even considering selling the ipad & mifi and buying a 3g model as it seems that's the simplest way to access the net via at&t ipad plans. But even this has me confused as some say that I will have to plug the ipad into itunes to get the latest carrier settings? I don't to take my laptop with me just to plug the ipad into. Hopefully somebody can help me or confirm what I've said is right or wrong.

Cheers