AT&T is scrambling to beef up its capacity at Austin's South by Southwest (SXSW) conference in response to the number of iPhone users at the event. The cell carrier's coverage -- which was already seen by many as limited in the area -- was knocked to its knees by heavy iPhone use at the conference and music festival, according to Silicone Alley Insider.

AT&T called the demand for voice and data access at the event "unprecedented," and said that it was working Sunday to ramp up its availability in the area around conference.

"These efforts are ongoing, but we anticipate that customers should see improved network performance [Sunday] evening and for the remainder of the event," AT&T said. "We will continue to monitor network performance throughout the event, and will do everything possible to maximize network performance throughout."

The carrier's service has been criticized for what many see as spotty coverage in the Austin, Texas area, even during normal usage times despite the company's service map that shows strong voice and data coverage throughout the city. 3G wireless data service, for example, is unreliable in some areas, dropping customers back to the slower EDGE service.

The extra demand on AT&T's service isn't simply because of the number of people attending SXSW. The carrier is seeing an overload because of the number of people using Web-based services like Twitter and Facebook to talk about the event in real time, too.

This isn't the first time AT&T has had trouble keeping up with customer demand at an event. The first Macworld Expo in San Francisco following the iPhone's initial release suffered from wireless data access problems even though users were limited to only AT&T's EDGE service. The company has since ramped up its ability to add support for special events, and that new-found skill is being put to the test right now in Austin -- hopefully with results that will make SXSW attendees happy.