When I first registered my iPad on AT&T’s 3G data network, I opted for the 250 MB for $14.99 per month plan to see whether I could live within the 250 MB limit. On the first full day that I used the plan, I blew through 100 MB, and it was not looking good for me making it through 30 days. I made it until 10 days before I received a notification on my iPad that I had 20 percent of my data left, and I was asked whether I wanted to add more data or upgrade my plan. A couple of days later I received the 10 percent notification, at which point I decided to switch to the unlimited $29.99 per month plan.
The process of switching plans is straight forward. When I received the notification and decided to upgrade, the Cellular Data settings page opened and I entered my AT&T account password. At that point I had the option of buying another 250 MB for $15, or upgrade to the unlimited plan. After I finished the process of confirming that I wanted to upgrade the plan, I saw a confusing message that basically said the change in the plan would not take affect until the next billing date.
I assumed the next billing date was one month from when I originally signed up for the 250 MB plan, which meant that I would go for more than two weeks without 3G data. Because I didn’t know what else to do, I decided to use up what little data I had left on the original plan and live with only Wi-Fi until the month had elapsed. Another day later after using the 3G service I checked the Usage setting on the General settings page and found my total Cellular Data usage was over 250 MB, I then viewed my AT&T account information and it showed I was using the unlimited plan and had 27 days left on that plan. Apparently, despite the message that I received when I changed the plan, the switch to the unlimited plan took affect immediately, which is what I was hoping for in the first place.