When the original iPhone came out, a non-contract/prepaid ATnT GoPhone plan was available for users who didn't want to sign up for a two-year commitment. This plan enabled users to pay approximately $20/month for unlimited data plus pay-as-you-go voice time usage, and the users could opt to cancel the plan at any time without paying an early termination fee.
No such GoPhone option was offered for the iPhone 3G or 3GS, but many people still own the original iPhone and are happily using the associated GoPhone plan to this day... or maybe not.
According to an article on TUAW and a confusingly ambiguous official statement from AT&T, it appears that GoPhone data plans will stop working on Wednesday 6/17/09, with many GoPhone users reporting the following message from AT&T just a couple of days before the change is expected to take place:
The change will coincide with the release of iPhone OS 3.0, but it appears that, although AT&T would like you to think the update is to blame, apparently GoPhone data plans may stop working for all prepaid iPhone customers, regardless of whether they upgrade to the new OS.
In short, it appears that if you have a first-gen iPhone on a prepaid GoPhone plan, then you have until Wednesday to sign up for a postpaid account, which requires a two-year commitment even if you choose not to buy a new iPhone, or else your data plan will likely stop working.
This news has come as a shock to many, including several people who feel that they have been loyal customers AT&T for two years and are now being punished as a result.