T-Mobile has clearly been making ATT nervous — witness the stunning preemptive strike that ATT made late last week when it said that it would give up to $450 to T-Mobile subscribers who switched to its service. Now T-Mobile has started taking some aggressive steps to address the biggest weakness in its war against ATT, Verizon and Sprint: Its wireless network quality. T-Mobile on Monday said that it is paying Verizon roughly $2.37 billion in exchange for spectrum on the coveted 700MHz band that it will use to boost its LTE coverage. T-Mobile says that the spectrum covers more than 150 million people in the United States and will give a particular boost to in-building coverage. The one issue for