The South By Southwest music/film/interactive festival in Austin was attended by so many iPhone users, AT&T had problems keeping the network working.
According to Daniel Terdiman at CNET, "it was nearly impossible to call anyone inside the Austin Convention
Center because the cell service was so poor. And because it seemed like
nearly everyone at the conference has an iPhone, that meant that very
few phone calls were going through."
Sunday night, AT&T said that it was trying to improve capacity with this statement:
"To accommodate unprecedented demand for mobile data and voice
applications at SXSW, we are actively working this afternoon to add
capacity to our cell sites serving downtown Austin. These efforts are
ongoing, but we anticipate that customers should see improved network
performance this evening and for the remainder of the event. We will
continue to monitor network performance throughout the event, and will
do everything possible to maximize network performance throughout. We
apologize to customers who were inconvenienced during this surge in
local network demand."
Instead of rolling out COW (Cells on Wheels) they tried to move the overload to other parts of the system that apparently did not work.
Most of reports and Tweets from iPhone users complaining were from
users connected SXSW Wi-Fi network. Recent research showed that that
about 42% of iPhone data is sent by WI-Fi.
Services provided by other wireless carriers worked fin.