Hoping to dispel its reputation for terrible reliability, AT&T today revealed the dramatic extent of its network improvements in 2011 as part of its fourth quarter earnings announcement.

The carrier said it made over 150,000 improvements throughout last year, including the addition of more than 700,000 square miles of 3G coverage. AT&T also said that 3G call retainability across the nation is up 25 percent from last year.

The latter is something I’ve definitely noticed while using my iPhone in Brooklyn and Manhattan. It used to be that I would drop about 30 percent of my calls when traversing the city; now a dropped call is a rarity. AT&T boasts that its 3G call retainability has been above 99 percent since the middle of September.

AT&T said that 80 percent of its mobile traffic now goes over its enhanced backhaul, which refers to its HSPA+ network that powers non-LTE 4G devices. For most customers, that means slightly faster speeds than 3G, but nowhere near the improvement that LTE would bring. Technically, the iPhone 4S is a 4G device on AT&T’s network, since it supports 16 megabits per second HSPA+.

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