If you’ve been enjoying unlimited wireless data access through the GoPhone back-door on AT&T’s network, you’d better enjoy the heck out of it between now and November 12th. That’s the date that this little loophole gets closed says PhoneNews, who got the info from the AT&T GoPhone call center.With a move like this, AT&T would try to stop people from getting a much less expensive data plan. Under current conditions, people buy an AT&T GoPhone which includes a SIM card. The cheap phone essentially gets tossed because the SIM card is the valuable nugget. A quick call to AT&T enables the SIM for the $20 monthly data plan, which is far less expensive than AT&T’s $60 plans that offer 5GB of data per month and is contract-free. AT&T indicates that they’re evaluating other ways to offer pre-paid data, but something tells me they’re going to drag their feet on that. Or when it does appear, it will be a very limited plan in terms of data since it was cannibalizing their traditional data offerings.