I have seen it posted both ways(the instructions that is). It seems there are many things that are really a case by case basis. Success has been had both with both methods.More below.
Are you saying you had the 200mb plan and switched to the 2g, and did the activation process and re-selected the 200mb plan again instead of the unlimited plan. Yes you are missing something, or your leaving out a part of the process thats making me miss something. Did you follow the instructions. Post everything you did. If you activated through iTunes after restoring the 2g, you should have selected the unlimited plan. If you are saying you did that but did not get any options to select a data plan, at all, my best guess would be that you didn't use a brand new unactivated sim card and just popped your current sim card into the 2g before going through the process in iTunes, is that what happened? Im sure you missed something, or everything perhaps, what exactly i can't be sure of but will try to help you narrow it down if you post more details on exactly what your process was, to the best of my abilities at least considering i haven't done it yet.
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Alright, you seem really knowledgeable so hopefully you can help. I plugged in my iPhone 2G with a new SIM card that picked up from the AT&T store. I began the activation process and got stuck at "activation requires additional time" so I called 611 and the CSR helped activate it. At that point, I hadn't been asked to choose a data plan yet. The phone was still in "connect to iTunes mode" and iTunes wasn't being cooperative and saying my phone's activation was still processing even though I could see I had service and had gotten a text message. The CSR pretty much got it activated and called the phone to confirm it but iTunes wasn't letting me proceed to the next step.
Since I needed to jailbreak it, I just used Pwnagetool while it was in "connect to iTunes" mode. I think this is where I screwed up because now my phone is jailbroken and in working order but I may have bypassed the step where I choose the data plan. I'm going to call AT&T tomorrow to see if I can do it over the phone since I can't do it online or through iTunes.
Any better options would be much appreciated.