CHICAGO -- Machine-to-machine (M2M) communications is emerging as an important growth area in wireless, but there's a battle underway over which network is best suited to accommodate the expected onslaught of connected devices.

The "we're all in it together" attitude quickly wore off at a carrier panel yesterday at Connected World magazine's conference in Chicago. The panel included the heads of M2M at AT&T Inc. (NYSE: T), Verizon Wireless , Sprint Corp. (NYSE: S), and T-Mobile US Inc. , and they quickly went into attack-and-defend mode when it came to questions about 4G.

WiMax may be losing ground to competing, although not yet deployed, technology long-term evolution (LTE), but Wayne Ward, vice president of emerging solutions at Sprint, believes it has a place in the verticals that M2M supports. There will be around 40,000 4G M2M cellular modules shipped in 2010, all of which will be based on WiMax, according to ABI Research . That's a bragging right that LTE can't yet claim. (See BWA Auction Is Bad News for WiMax's Future .)

Larger-scale applications such as fleet management, security, digital signage, and -- of course -- video could benefit from the bandwidth and low latency that WiMax offers. Sprint has also been pushing and, in some cases, trialing its WiMax networks for large smart-grid deployments as well. The network may be overkill for most meter pinging use cases today, but eventually, the kind of advanced metering infrastructure and demand response apps that utilities are promising could require it.

Ward stressed that by having every network from iDEN and EV-DO 1x to WiMax available today, an M2M developer working with Sprint can match the network to the requirements and price it accordingly -- no overkill or underkill.

"We have 4G today -- we have subscribers and revenues while others are just talking about it," Ward said in a jab against Verizon. "Let's leave it at that."

Verizon's director of open development, Maurice Thompson, didn't leave it at that, but he did agree that M2M is not a one-network-fits-all scenario. He said Verizon isn't looking to fit every customer into its upcoming LTE network nor force-fit them into the present network. Rather, the networks are tailored to the apps' needs. A small, bursty SMS app might only use 2G, while a robust video streaming app might need LTE, he added.

For a scenario that would require LTE's low latency, Thompson suggested gaming. If a child is participating in a multiplayer game, it's important he has the same experience playing while riding the bus as his friend sitting stationary at home does. So if, for example, he makes a shot in a basketball game, the point is reflected to the player at home without any delay.

In the future, these apps may not be confined to one network either. Hamish Caldwell, executive director of mobility product management at AT&T, said that while most apps rely on a single network today, that could change as the use cases become more complex.

The transition from one network to another could happen seamlessly for consumers, or as in the gaming example, could be tied to the game. Thompson suggested the game developer could adjust the game to take advantage of the faster network, and the consumer would understand he had transitioned from 3G to 4G.

To accommodate this need for multiple networks, Caldwell stressed the importance of operating both a wireline and wireless network, while the other carrier representatives harped more on what kind of wireless network is needed. Both Caldwell and John Horn, national director of M2M for T-Mobile, emphasized the importance of the global reach that GSM affords.

"These two like to have fun with their maps," T-Mobile's Horn said, referring to AT&T and Verizon, "but the truth is the red map looks better than the blue one."

Horn cited stats saying 87 percent of the world runs on a GSM network and is migrating towards HSPA+, as T-Mobile is. He also stated (repeatedly) that HSPA+ has run faster than Sprint's WiMax networks in multiple tests. (See T-Mobile USA Expands HSPA+ and HSPA+ in the US & the Wait for Handsets.)

"The nice thing about GSM is you don't have to choose between a network; you have most of the world on the same network, which drives down costs," Horn said. "When you are in an EDGE area, it runs EDGE. In GPRS it runs GPRS, so there's total network compatibility. When you look at network costs, speeds, and what you are trying to accomplish, I can only see one solution."

Verizon does have access to GSM abroad through its partial owner, Vodafone Group plc (NYSE: VOD), and a partnership with Qualcomm Inc. (Nasdaq: QCOM) for NPhase. That makes Verizon a global force for M2M, Thompson said. Indeed, the first quarter of the year was the first time Verizon broke out "other connections" on its network, and it is already coming in ahead of AT&T.

AT&T more than doubled its connections at 5.78 million in the first quarter, up from 2.8 million last year. But Verizon reported 7.3 million other connections on its network in the quarter. Neither company broke down the device mix. (See Smartphone Data Makes Verizon Look Smart and AT&T Stays Mum on Tiered Mobile Data Pricing.)

Right now, the rising tide is still lifting all boats, and the carriers agreed there's room for all the players, as well as for mobile virtual network operators that can claim the benefit of aggregating all networks together into one offering. With Berg Insight AB predicting that operator revenues for M2M will reach $12.9 billion in 2012, all the carriers agreed they want a part of the growth, on any network. (See M2M Pits Carriers Against MVNOs.)

"We are at the beginning of a journey that's going to be a hot, fast growth curve for all of us," Sprint's Ward concluded.

— Sarah Reedy, Senior Reporter, Light Reading Mobile