Qualcomm has been running its new EV-DO technology through the wringer and promises the first fully voice-over-IP-ready radio access network for the first Revision A deployments this fall. But one question still hangs in the air: Even though the end-to-end VoIP is now a reality, will carriers want it?

Although VoIP has pervaded every other network in telecom — enterprise, broadband, Wi-Fi, transport and switching — the benefits of VoIP in the last link of the wireless network — the air interface — aren't so clear. Cellular voice has always been a capacity game. For the last two decades, vendors and standards bodies have become obsessed with the task of cramming one more conversation onto the same finite amount of radio spectrum. And despite misconceptions to the opposite, VoIP isn't a capacity saver. In fact, it's a capacity hog on the access side — something of little consequence when you have a dedicated DSL line, but a grave concern when you're dealing with a 1.25 MHz channel of PCS spectrum.

Qualcomm, however, has been tinkering with its air interface, adding new receive diversity techniques to revision A that will deliver some gains in capacity making its initial VoIP over EV-DO slightly more spectrally efficient than its circuit-switched CDMA 1X counterpart. But Samir Khazaka, senior director of technical marketing, readily admits that those same technical improvements could be as easily applied to 1X as they are to Revision A networks, nullifying any capacity gain. In fact, Qualcomm isn't arguing VoIP will add capacity to the network — far from it.

Qualcomm is touting VoIP for VoIP's sake. If carriers don't stand to lose any voice capacity in the network, then they're free to decide VoIP for its own merits, Khazaka said.

“Compared to 1X, Rev. A has fairly equivalent voice capacity,” Khazaka said. “The exciting thing here is we're delivering good-quality VoIP without sacrificing capacity. It becomes a more flexible way to deliver voice services.”

The advantages of VoIP over circuit-switched voice are obvious to carriers looking to widen their ever-shrinking voice margins. Since VoIP becomes part of the data stream, the service allows for simultaneous voice and data transmission. It allows voice to be added to data applications, making possible services like video telephony, simultaneous conversation and multimedia messaging and even IP push-to-talk.

Perhaps most significantly, it breaks down that formidable barrier between voice and data communication on the phone, linking such widely used functions as presence and graphical interfaces to any voice application, Khazaka said.

But even if carriers can launch VoIP without losing voice capacity, there's still the question of the billions of dollars they've already invested in circuit-switched networks over the years. While Sprint and Verizon Wireless now both have extensive EV-DO networks covering most of the major metropolitan areas, they have far more extensive CDMA 1X networks.

IPWireless has shipped its all-IP cellular equipment to dozens of customers, and although its system fully supports VoIP, very few of its broadband access customers and none of its mobile cellular customers have used it, said Jon Hambidge, vice president of marketing for the vendor. Like EV-DO, IPWireless' time division-CDMA solution is used to add data capacity to a voice-centric network, Hambidge said, but carriers already have highly optimized voice networks in place.

“How do you compare the cost of a call that has no incremental capex or opex with a call that requires new investment in the network?” Hambidge asked. “It's no longer a question of sending a call cheaper. Carriers have already made the investments. They're sunken costs at this point.”

Another concern for carriers is that a VoIP-capable network would be an invitation to the competition. Outside providers could undercut their voice prices and siphon off their already-threatened voice revenues. But carriers already have been fairly successful in blocking other users' voice packets. Many independent VoIP carriers have tried to use all-you-can-eat data plans offered by 3G operators to offer VoIP but have been blocked at every turn, said Eric Hernandez, CEO of Solegy, a managed services provider that sells VoIP and IP multimedia subsystem (IMS) services to small businesses.

Carriers can encrypt their own voice traffic, then block all non-encrypted packets. And while there are some tricks a competitor could use to disguise its voice packets as mere data packets, many carriers have simply begun introducing incremental jitter and delay that would have little effect on a data transmission but would absolutely distort a voice call, Hernandez said.

“They're already taking very real steps to make sure their data plans are not being used to make voice calls,” Hernandez said. “I don't see any reason why a voice carrier wouldn't be able to block any outside voice traffic in the future.”

Although both Sprint and Verizon Wireless have committed to upgrading their networks to EV-DO Rev. A next year, that doesn't necessarily mean they're embracing VoIP. Rev. A offers greater data capacity than EV-DO Rev. 0, especially on the upstream, enabling technologies like two-way video. Its quality-of-service attributes also can be used for other applications besides VoIP, such as multi-player gaming and offering priority access to enterprise customers.

Even if VoIP was on the top of the list, there is the issue with handsets — very few of them are capable of making a VoIP call. But that situation is changing as vendors start producing more session initiation protocol phones to support IMS deployments in the next few years, said Steve Shaw, director of marketing for unlicensed mobile access vendor Kineto Wireless.

“Most handsets now already come with an IP stack,” Shaw said. “The phones already have 75% of what's needed to support VoIP.”

No one expects Sprint and Verizon Wireless to flip a switch one day, turning on an all-IP network. VoIP is expected to come in phases. Qualcomm's Khazaka said applications like video telephony and push-to-talk will likely be the first to take advantage of the new technology, combining voice with other network elements, making them ideal for an all-IP environment.

Carriers may also find that many enhanced voice applications, such as enterprise PBX services, will be easier to run on IP instead of over a circuit.

That's when the transition will start happening, Khazaka said. Once a customer has those applications on the phones, there's nothing to stop the carrier from transitioning their regular voice service over to the same IP channel.

“Launching Rev. A is a multi-faceted decision — it's not just a VoIP-driven one,” Khazaka said. “But as you introduce these new applications to the network, they will have voice components. A certain proportion of the traffic on the network will be VoIP by default. As the need for voice capacity arises, why not add that capacity with VoIP?”