Tony Smith asks and answers … WTF is... VoLTE:
How are the UK's mobile network operators going to handle voice calls when they switch on their 4G LTE networks? Possibly not very well.
LTE is a purely IP network, so ordinary phone calls need to carried using voice-over-IP (VoIP) technology. That ought to be straightforward: VoIP has been around for years, the principles are understood, and there's even an LTE-centric VoIP specification, Voice over LTE (VoLTE), formerly known as OneVoice. It sits on top of the well-established IMS (IP Multimedia Subsystem) standard.
The problem is, VoLTE isn't an easy technology to deploy. It's very new and there's still a lot of testing going on in the lab. Part of the problem is that its implementation is very network dependent: what kit the operators are using, how big the network is, what backhaul capacity they have, the impact of the extra VoIP on the data network, and so on.