Outside the C Block and apart from the major operators, the technology path that spectrum winners will pursue is likely to be a mixed bag. Policy-makers will have to go back to the drawing board to determine the outcome for the D Block. That 10 MHz span was envisioned as a shared private and public safety network, but it did not receive the minimum bid set by the FCC. The 6 MHz E Block, meanwhile, may be a special case. Most of that spectrum was won by either Qualcomm or Frontier Wireless, a unit of direct broadcast satellite company EchoStar. Qualcomm is expected to use the spectrum to augment its MediaFLO mobile broadcast service, and EchoStar is likely to follow a similar strategy.

That leaves the A and B blocks, both of which include 12 MHz of spectrum and are based on smaller geographic territories than the C Block. Aside from AT&T and Verizon, which won some A Block licenses, most of this spectrum landed in the hands of smaller incumbent mobile operators — and whether they will deploy 3G or 4G technologies is a matter of debate.

“They could use 3G today to enhance their existing networks by providing more spectrum,” Nortel's Locklear said. “Or they could … deploy what's being used by the larger carriers in order to be their roaming partners.”

Small incumbent wireless carriers receive substantial revenues from roaming agreements with major national carriers, and they will see new roaming opportunities as major carriers deploy 4G networks. But Mukerjee believes the smaller winners of the A and B blocks are likely to deploy 3G initially because those blocks are narrower, limiting the data rates they can offer and making the business case for 4G less compelling than at the C Block.

Stakeholders are reluctant to forecast what service providers will spend on 700 MHz deployments — in part because strong take rates could erode the cost advantage provided by the spectrum's excellent propagation characteristics.

Andrew Seybold, founder and principal of the consulting firm that bears his name, estimated that about 25,000 cell sites would be needed to cover 75% of the country at 700 MHz. “To cover the same area on a 2.5 GHz WiMAX network, you would need 65,000 cell sites,” he said.

That means a 700 MHz network could be faster to deploy and cost less, at least initially. But as Seybold pointed out, “cell sites are closer together at 2.5 GHz, which means you get more network capacity.”

As traffic at 700 MHz builds, the only way to get additional capacity is to start building more cell sites closer together, which eventually could erode the 700 MHz cost advantage — in populous areas, at least.

The investment required to build 700 MHz networks also will depend on the extent to which incumbent cellular operators will be able to leverage their existing network investment. Electronics typically represent 35% to 40% of the cost of a network buildout, Wright said. “The rest is land, building and towers, and for incumbent operators, one of the advantages they have is they have existing land, building and towers,” he said.

Certain factors will tend to make 4G deployments at 700 MHz less costly than earlier-generation deployments, Wright added. “The electronics compared to CDMA will be a whole lot less,” he said. “The electronics we use in WiMAX and LTE are a fraction of the size. You get a whole lot more [millions of instructions per second] and memory on much smaller semiconductors than you did in the past. They dissipate less heat so they use more compact boxes, which will significantly simplify size and the cost of deployment.”

Where network operators may see their deployment costs rise, however, is in the backhaul network. “It's not uncommon to have a cell site with one or two T-1s to handle all the traffic,” Wright said. “In broadband systems, it will take seven to 10 T-1s to provide a minimum amount of backhaul.” Overall, he predicted that “the backhaul cost will be significant in the buildout of next-generation networks, and carriers will be looking at different technologies.”

U.S. operators traditionally have made minimal use of wireless backhaul, but that could change, Wright said. He foresees increased interest in wireless backhaul as U.S. operators seek creative solutions to their new backhaul challenges.

In the core network, IP will underlie mobile broadband networks, regardless of whether they are based on LTE, UMB or WiMAX. As a result, carriers that have invested heavily to migrate their existing core networks to IP will be rewarded, Alcatel-Lucent's Mukerjee said. “If your underlying core network is IP, you have a definite cost and service-delivery advantage that cannot be easily replicated,” he said.

Longer term, network operators deploying service at 700 MHz also may benefit from increased economies of scale as other countries open the spectrum for mobile broadband. Although few countries have announced specific plans, Seybold noted, “There is a lot of momentum in the U.N. and the ITU.”