First, they respond quickly to messages. A good thing! ^

I had asked them about tethering with an iPhone 4, and they said no, that would not work unless jailbroken, and mentioned there are apps on Cydia that would do the trick.

I'm thinking my best bet is going to be to jailbreak my old 3G phone, install a tethering app on it, and use the iPhoneTrip sim. Since that phone is not in any way connected to AT&T contractually, and since AT&T cannot claim to own it in any way shape or form, there's not much to go wrong. And I can use it as a mobile mifi gadget, if I'm understanding things correctly.