­Most of the largest U.S. operators are already well advanced in their LTE network rollouts. Others may lag behind, but LTE deployments overall are still progressing quickly -- perhaps more quickly than could have been foreseen 12 to 18 months ago. Additionally the U.S. market already has more than a half dozen LTE-capable smartphones and tablets with many more to follow by year-end 2012 -- and still more in calendar 2013.

iGR says that it fully expects LTE uptake to grow quickly. Once the LTE subscriber base starts to grow, more devices become available and usage of the network increases, then the operator increases the network capacity.

Between 2012 and 2016, iGR forecasts total U.S. LTE infrastructure capital expenditures to be $39.82 billion, based on the anticipated growth of LTE subscribers and data traffic on the networks. iGR's LTE cost model is based on the amount of data the network is able to support and deliver. The cost model is based on the cost required to add 1 GB of data capacity to the network.

"Operators are continually balancing their network CapEx between coverage and capacity," said Iain Gillott, president and founder of iGR. "The engineers strive to provide sufficient coverage to be competitive and sufficient capacity to meet the needs of the (hopefully) growing subscriber base, while minimizing unnecessary CapEx. This report clearly shows there remains a significant opportunity in the U.S. LTE infrastructure market."