Project yourself into the future – let's say mid-2012. It's been about a year and a half since Verizon Wireless first launched its LTE network in December 2010, and after a long wait, the company has finally come out with the first smartphone running voice over LTE (VoLTE) technology.

You go out and buy the device, turning it on the second you have it out of the box. One of the first things you notice: The phone's native voice application isn't limited to just voice. It has an option for video calls, and there's also an option to send multimedia messages, along with presence indicators that show when people on your contact list can participate in a video call.

This is what VoLTE can do.

When operators add voice capabilities to their LTE networks, they're not just installing voice over LTE (VoLTE) technology to their IMS infrastructure. They're rolling out a service that will fundamentally change how their customers communicate.

Marjorie Hsu"Can you hear me now will become 'Can you see me now'," says Verizon Wireless product development executive Marjorie Hsu, referring to the company's marketing for its 3G voice services. "We're not selling the technology; we're selling the services and the user experience."

Verizon won't limit itself to just routing voice calls over its LTE network when it comes out with its first VoLTE phones next year.

Hsu says Verizon plans to equip its VoLTE handsets with native applications rivaling those provided by over-the-top players like Skype, such as video chat, multimedia messaging and presence indicators similar to those found on instant message services.

"We're very excited about VoLTE and video communications," Hsu says. "IMS and LTE will really allow us to drive a richer customer experience that starts to be competitive against some of the over-the-top alternatives today."

VoLTE also will allow Verizon to offer customers simultaneous voice and data services, a capability lacking from its current LTE and CDMA deployments.

Verizon is currently conducting trials of VoLTE and plans to come out with handsets compatible with the technology some time in mid-2012. Don't expect the "can you see me now" tagline to appear in commercials any time soon – Hsu says it's being bandied about by the teams working to roll out VoLTE, not by Verizon's marketing department.

MetroPCS also plans to come out with VoLTE next year, though its motivations are slightly different than Verizon's. The bandwidth-strapped regional carrier wants to migrate its customer base to LTE as soon as possible so it can reuse the spectrum in its legacy CDMA network for LTE. To do that, it has to make sure its LTE network can handle voice as well as data.

Ed Chao"Voice over LTE allows us to gracefully migrate off CDMA over time in a way that's non-disruptive to our customers," says MetroPCS network operations chief Ed Chao.

Aside from the need to decommission its legacy network, MetroPCS was also attracted to VoLTE for the same reason Verizon was: its multimedia capabilities. VoLTE will allow MetroPCS to install services on handsets that previously had to be handled by third-party apps, like video calls.

"It allows us to do more integrated multimedia communication services for our customers," Chao says. "Video calling is certainly one possibility, and there's other value-added services you can add in with VoLTE service... These are things that are more easily supported on IMS core than if you're trying to cobble a number of other solutions together with your circuit-based core."

Unlike the generations of technology that have come before it, LTE is tailored for data traffic and doesn't have inherent voice capabilities. Operators basically have two choices for LTE smartphones: They can route calls over their legacy networks with technologies like circuit switch fallback, which is currently handling voice calls on the LTE smartphones at MetroPCS and Verizon, or they can deploy VoLTE.

Most operators will eventually opt for the VoLTE route because it's ultimately more simple and cost effective than sending voice calls over their legacy networks and will allow them to more easily phase out legacy networks.

Getting Down to Nuts and Bolts
The industry has known for years that LTE, with its fast speeds, low latency and higher degrees of efficiency, would fundamentally improve wireless service. Adding VoLTE to LTE could bring about another major shakeup with wireless service as operators add multimedia capabilities to everyday voice communications.

However, moving VoLTE from concept stage to reality is not going to be a simple task.  Operators must tackle how to handle handoff between VoLTE calls and their legacy networks, as well as work with handset manufacturers on VoLTE-equipped smartphones.

Handoff between LTE and legacy 3G networks can be done by installing Single Radio Voice Call Continuity (SRVCC) technology, which allows calls to transfer from LTE to 3G without interruption.

However, the handoff technology adds a considerable degree of complexity to both handsets and networks, and not everyone has decided to deploy the technology.

Verizon, for one, has decided to opt out of the additional complexity of handing off its VoLTE calls to its legacy network.

Hsu says the company doesn't plan to install technology that would let VoLTE calls transfer to its CDMA network. VoLTE calls will be able to roam onto other LTE networks, but they won't hand down to Verizon's CDMA network. The company's current LTE smartphones route voice calls over its CDMA network using circuit switched fallback.

As a result, if a Verizon customer places a VoLTE call and then proceeds to travel outside of Verizon's LTE footprint, the call will drop unless it can be handed off to another LTE network.

This probably won't be much of a problem: Hsu says the company plans to hold off bringing VoLTE phones to market until its LTE network has a large enough footprint to avoid dropped calls. Verizon is aggressively expanding its LTE network, and plans to cover more than 145 markets by the end of this year. When it launches its first VoLTE smartphones next year, the company's LTE footprint should be well on its way to matching the coverage of its 3G network.

Shubh Agarwal, marketing executive at Mavenir Systems, says he's not surprised to hear Verizon has decided to deploy VoLTE without handoff to its legacy CDMA network.

"Operators are planning for more wide-area LTE coverage, so this handoff problem will only be seen at the edges for 3 percent to 5 percent of calls," he says. "It's cheaper for them to deploy a couple more base stations than do this complex network that does funny handover between the two domains."

MetroPCS hasn't decided whether to hand off VoLTE calls to LTE. AT&T and U.S. Cellular, which are in the process of rolling out their own LTE networks, declined to comment on their VoLTE plans.

Operators also will have to grapple with different scenarios for transferring VoLTE calls to other LTE networks. This could prove difficult in the near term, as not all operators have decided to deploy VoLTE on their networks.

Getting VoLTE service out to customers takes more than just installing the necessary network equipment. Considerable work also needs to be done on the handset side.

Bringing a VoLTE-capable smartphone to market isn't as simple as just making the device compatible with the service – the hardware and the phone's user interface have to be tailored to VoLTE's capabilities.

Both Verizon and MetroPCS said their current LTE smartphones will not be compatible with VoLTE, and for good reason. Front- and rear-facing cameras are necessary to support video calls; the devices will need to have superb battery life and super-fast processors to keep up with the demands of multimedia; and a special user interface to make multimedia VoLTE calls as simple as the tried-and-true voice capability of their predecessors.

Reviving IMS
VoLTE's secret sauce is the IMS infrastructure some operators have installed to support their LTE networks. With IMS already in the network, it's just a matter of installing the necessary application servers to make LTE-based voice, video calls and other services available on the network.

IMS is a technology that has been through the high end and the low end of the hype cycle.

When IMS first emerged around 2006, it was touted as a way to get multimedia content onto 3G networks and converge operators' fixed and mobile offerings. Enthusiasm for the technology quickly died when it became clear that it would be expensive and complicated to install, with limited usefulness or potential for return on investment.

With the advent of LTE networks, however, IMS is experiencing something of a revival. Operators like Verizon built IMS into the foundation of their LTE network, allowing IMS-based applications for voice and multimedia to be relatively easily deployed. The development of IMS-based applications has lagged behind LTE and is playing catch up, but there's a new level of interest in the once-derided technology.

GSM Association (GSMA) Technology Director Dan Warren, who headed the group's effort to standardize voice service over LTE networks, expects VoLTE deployments to become more common as the technology matures.

"If you ask me in three years time, absolutely, people will be launching LTE networks with VoLTE capabilities from day one," Warren says.

Infrastructure vendors also have seen increased interest in the technology.

"VoLTE is going to be the springboard for IMS to take off in a bigger way," says Mohan Trikur, who heads the VoLTE program for Ericsson in North America. "It was hard to find a business case for IMS. VoLTE makes IMS for much more than voice, so IMS becomes much more interesting to operators."

Ken Wirth, who heads end-to-end wireless solutions at Alcatel-Lucent, agrees with Trikur's synopsis.

"Now, after all these years, we finally have the killer application for IMS," Wirth says, referring to VoLTE. Alcatel-Lucent was selected to provide the IMS component of Verizon's LTE network and is currently conducting "detailed" VoLTE trials with the operator.

Wirth says Verizon will probably launch VoLTE around this time next year and the industry will "probably see AT&T follow suit in a very similar manner." Alcatel-Lucent provides the IMS core for AT&T's U-Verse voice service and has made a bid to supply IMS for the operator's LTE network.

"The reason we haven't seen a lot of IMS deployments to date is because IMS was a solution looking for a problem," Wirth says. "Once you've got some applications that justify the cost... the economics for the operators start to move in a positive direction."

"Revolutionize" is probably too strong a word to describe what VoLTE will do for the next generation of wireless communications, but it's not too far off the mark.

VoLTE and the key IMS technology that supports it will allow operators to change the way their customers place calls. Customers won't have to launch a third-party application to place a video call, since video chat will be made as seamless as voice calls. Other possibilities for IMS abound, such as video collaboration services for business customers.

The combination of IMS and LTE is a force to be reckoned with, and VoLTE is just the beginning.