Anyone who expected the first smartphones that support voice over LTE (VoLTE) to be launched at the Consumer Electronics Show in Las Vegas last week have hopefully already recovered from the disappointment.

Given that the first commercial launches of the IMS-based VoLTE services are expected in 2012, the world's biggest gadget show at the start of the year seemed like a logical place to launch devices that will support mobile operators' next-generation voice services on LTE networks. That has turned out not to be the case. (See Operators Raise Voice Services on LTE .)

But the lack of VoLTE-capable smartphones on the market does not necessarily mean that the technology is behind schedule. Analysts say that the technology is developing as expected with operators, equipment manufacturers and device makers.

For example, Gabriel Brown, senior analyst at Heavy Reading , says the first VoLTE services will launch sometime in mid- to late-2012.

"I expect services to launch in 2012, led by North American operators with a CDMA heritage, and perhaps some advanced Korean operators," he said. "For operators with a UMTS heritage, we expect commercial launch from 2013."

According to Joss Gillet, senior analyst at the GSM Association (GSMA) 's Wireless Intelligence unit, "VoLTE will come in the second half of this year when we'll have both networks and devices compatible."

The operator that many expect to be first with commercial VoLTE services is MetroPCS Inc. (NYSE: PCS), followed by Verizon Wireless . Indeed, MetroPCS has said that it hopes to launch the services in the early part of this year. Last week, the regional U.S. operator launched two new Android LTE smartphones at the CES show, but neither will support VoLTE when they become available, according to an operator spokesman. (See MetroPCS Adds 2 LTE Androids, MetroPCS: $100 LTE Smartphones in 2012? and MetroPCS Plots LTE Smartphones, VoLTE Trials.)

One of the issues with getting device support for VoLTE has to do with how to integrate the IP Multimedia Subsystem (IMS) stack, according to Dan Warren, director of technology at the GSM Association (GSMA) . "A question that comes up is where the IMS stack resides … encompassed in the OS or more tightly integrated into the device hardware itself," he explained.

But wait, there's more
Device support isn't the only challenge for VoLTE.

As outlined by Heavy Reading's Brown in the recent Light Reading webinar Voice Over LTE: A Foundation Service for All-IP Mobile Networks, VoLTE touches every part of the LTE and legacy networks and requires tight integration across all of those parts, including the radio link, packet network, service core, devices and the legacy network. Implementing a new technology that has such a pervasive impact on the network isn't likely to happen overnight.

More specifically, one of the more challenging aspects of VoLTE that operators are grappling with now is the feature called single radio voice call continuity (SRVCC), which enables calls to be handed from LTE to 3G or 3G networks. This functionality is essential for ensuring calls are not dropped when a user loses an LTE signal or moves out of LTE coverage while using a service.

"That's complicated to implement," noted GSMA's Warren, adding that there are "no concerns about VoLTE as a long-term prospect."

Getting SRVCC right is part of the reason why Heavy Reading's Brown thinks operators with UMTS legacy networks will launch VoLTE later than CDMA operators.

"These [UMTS] operators will typically want in-call handover from LTE to 3G, which brings additional technical challenges that are eased by a new generation of device chipset currently sampling to handset makers for use in test devices," said Brown.

Another issue for VoLTE is support for E911 services. In some markets, like the U.S., there is a regulatory requirement to be able to locate users.

Despite the many challenges facing VoLTE, the first commercial services are still expected this year. But it will only be the start for the technology that could underpin not only voice services but also various other media-rich services over operators' next-generation mobile networks.

— Michelle Donegan, European Editor, Light Reading Mobile