Bandwidth-hungry customers line up outside an AT&T store. In a new filing explaining why it wants to buy T-Mobile, AT&T essentially admits that its network wasn't ready for the iPhone, and won't be able to handle new smartphones and tablets as they come on board.

The filing says:

A smartphone generates 24 times the mobile data traffic of a conventional wireless phone, and the explosively popular iPad and similar tablet devices can generate traffic comparable to or even greater than a smartphone. AT&T’s mobile data volumes surged by a staggering 8,000% from 2007 to 2010, and as a result, AT&T faces network capacity constraints more severe than those of any other wireless provider.

Those dates aren't a coincidence. 2007 is when the iPhone was introduced as an AT&T exclusive.

AT&T warns the problem is getting worse as more consumers use video and enterprise apps on their smartphones, and guesses that its network will carry more traffic in the first five to seven weeks of 2015 than it did in all of 2010.

Then it says the T-Mobile deal:

...will thus benefit consumers by reducing the number of dropped and blocked calls, increasing data speeds, improving in-building coverage, and dramatically expanding deployment of next-generation mobile technology.

It's nice to see AT&T finally admitting it has a problem. One has to wonder why it didn't see this coming when it signed the iPhone deal in the first place, though.

A PDF of the filing is available here.