We haven’t tested this yet, so we can’t make any guarantees about the success you’ll have with it, but it seems there’s a way to change your iPhone data plans to unlimited for $30 a month.
Ok, let’s take a little breather now, because we might go missing after sharing this with you – messing with Apple is dangerous business.
For starters you need a “go” phone with an IMEI number (this is the number in the battery casing), which can be bought at most tech retail stores for about $30, your iPhone SIM information (find this in General > Settings > ICCID), and account access from AT&T.
The next step is to call AT&T and ask for the unlimited texting, email and data phone plan that is available for non-smartphones, and tell the operator that you’re going to switch from your iPhone and use an adapter to make the micro-SIM work.
Once you have the new account, make a call from your iPhone and the AT&T will switch back to it and send you some messages telling you to upgrade to a data plan for smartphones.
After a few hours you will get another message letting you know that you now have the unlimited 3G data plan. This last part may now work in some cases, and there’s a workaround involving a second call to AT&T, but that’s already far beyond the scope of this short overview, so if you’re going to try this make sure you check out all the details on the actual forum post.