Here's a press report I picked up recently from Kineto, who've ported their UMA protocol stack and application to Android Froyo. This may sound a bit cryptic but it has interesting implications for Voice over LTE.
For those of you who can't place the term UMA (Unlicensed Mobile Access), it's basically GSM voic calls over Wi-Fi. On the mobile device, all layers of the protocol stack of GSM are reused with the exception of the lowest layers where the UMA software introduces a switch so phone calls and signaling are either using the GSM infrastructure or a Wi-Fi access point that connects to the Internet. For the user its completely seamless. On the network side, the base station and the base station controler is replaced by a UMA gateway controler that connects to the Internet on the one side and to the network operator's core network on the other. To the core network the gateway looks like a GSM base station controler which makes UMA also transparent to the core network, i.e. no software or hardware chagnes needed there at all.
So UMA on Android, what does that have to do with voice over LTE? Well, as you might be aware of, there's no built in voice telephony functionality in LTE. That's why a number of different options have been suggested, one of them being Voice over LTE via GAN, or VoLGA for short. Now GAN (Generic Access Network) is just a synonym for UMA and that already tells most of the story. Volga replaces the Wi-Fi layer of UMA with LTE.
In other words, to close the circle, there's only little work required to modify the UMA Client for Android to use not only a Wi-Fi network but also an LTE network once Android LTE devices become available. With a client available for Android, operator based Voice over IP has arrived in the smarphone space (beyond RIM) and on an operating system that will play a major role in future LTE devices. And the work to make the software work with LTE is almost trivial since both Wi-Fi and LTE are IP based networks. So 99.9% of the software don't care if Wi-Fi or LTE is used for the transport of the IP packets that contain the speech data of an ongoing voice call.
One additional thing that requires a bit more work is the handover of an ongoing voice call from LTE to GSM (or UMTS) when the user is at the coverage limit of the LTE network. But like UMA, which is a 3GPP standardized technology, 3GPP also comes to help out here as there are already methods defined to do just that. The functionality is referred to a Single Radio Voice Call Continuity (SR-VCC). Specified in a generic way it can be used for IMS and also for Volga and potentially other solutions in the future.
While it takes a bit of work to implement SR-VCC into Volga, its fully specified and well worth to be done, as LTE – GSM handover of voice calls is a network operator's biggest asset to stay relevant in the voice call domain in the future as over the top voice applications have no way of doing that.