Smartphones generate 24% more mobile data trafic than the "dumbphone" and a Tablet (such as iPad) generates either equal or even greater to that of the smartphone. AT&T's data volume went up 8,000% from 2007 to 2010 thus giving the company more capacity restraints than any other wireless provider. The problem is surly getting worse for the market is now using more video and enterprise apps, the company guesses that the network traffic they carry will increase for the first five to seven weeks of 2015.
AT&T says that with the new 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 the next-generation mobile technology."
(had to add this)