Despite what mobile carriers have been saying about LTE's readiness, there is still a fundamental problem with the deployment of an all-data packet switched network: its incompatibility with the old circuit-switched networks. Though LTE will support a tremendous jump in data transmission speeds on our mobile devices, it still cannot support voice and SMS functionality because those are built on the old circuit switched architecture.
Currently, there are a few ways this problem can be tackled. There is IP Multimedia Subsystem (IMS), the 3GPP-endorsed way that delivers voice and SMS through IP architecture, sort of like a big VoIP system. There is network hybridization, where the 4G network would only handle data and the legacy 2G/3G networks would handle voice and SMS. Finally, there is VoLGA, or Voice over LTE via Generic Access, a spec based upon 3GPP's GAN standard, which allows circuit switched traffic to be piped into LTE packets.
VoLGA is backed by a group of wireless industry leaders such as Alcatel-Lucent, ZTE, Starent Networks, Nortel, and Ericsson, as well as consumer electronics companies LG, Motorola, Samsung, and Huawei, which are collectively known as the VoLGA Forum.
Deutsche Telekom/T-Mobile is the first of the wireless network operators to join the VoLGA forum, in the belief that a unified move is urgent. At the LTE World Forum in May, T-Mobile's core network architecture lead Franz Seiser said, "There's a big risk if we don't decide how to go forward with our cash cow...If we don't get this right, we could put the whole of LTE at risk."
If more carriers are unified behind VoLGA, it is more likely to be approved as a 3GPP standard, and the technology could then move forward. Even though it is already a 3GPP standard, IMS innovation is reportedly slow and costly.
The forum completed its second draft of the VoLGA spec in May, and hopes to be finished by the end of the year to submit it to 3GPP release 10, the LTE Advanced official standard.