It is easy to understand AT&T Inc.'s desire to add to the durability and density of its 4G network when you consider the sheer number of smartphones and other devices that will be on the air in the coming years. This Tuesday, AT&T said it sold more than 10 million smartphones in the fourth quarter, thanks to high demand for the iPhone and Android over the holiday period. This beats its previous record of 9.4 million smartphones in the same quarter in 2011. AT&T executives, meanwhile, have been in Las Vegas talking about the need to densify the 4G LTE network in big cities like New York, Chicago and San Francisco over the coming years. The operator has already laid out how it will do this as part of its plan to cover 300 million potential customers in the U.S. with LTE by the end of 2014. Additions to the network will include:

AT&T already has the fastest 4G cities in the country, but my read is that this network effort is not merely about the need for speed. The way its subscriber base is moving to smartphones and shared plans that encourage users to add devices like tablets to their data plans suggests ever greater waves of IP traffic carried over the network in the future. Certainly, AT&T can try and control that with data caps, but the carrier also wants people to use more data because that's the future of its revenue stream. So adding 4G density in cities, where people are most likely to burn their way through massive amounts of data, makes good sense. Particularly for a carrier like AT&T that didn't adequately foresee what would happen when the iPhone arrived on its 3G network. Will the drive for density be enough? It's hard to say, since we don't know how another device or multimedia app might once again change the rules for mobile network density. Bulking up 4G in cities just seems like a good idea for AT&T whatever happens, though, given the services it is hoping to layer onto the 4G network. — Dan Jones, Site Editor, Light Reading Mobile