T-Mobile, AT&T, and Verizon have all started, or will soon start, their roll out of VoLTE. VoLTE, or Voice over LTE, is an IP voice solution that is based on the IP Multimedia Subsystem (IMS). Using data for voice services comes with advantages, but it's not an easy solution to implement.
2G and 3G voice service is based on the circuit-switched (CS) domain. This is the traditional method that wireless carriers have used to connect voice calls and send text message over their networks. With the switch to LTE and an IP based solution, no provisions were made for how voice and texts would connect. There's something called circuit-switched fallback (CSFB) that, wait for it...falls back...to circuit-switched handling for voice, but this is not a perfect solution. CSFB connects the call and then hands it off to the VoLTE protocol, but there's a delay of up to 2 seconds in connecting. This can lead to a poor customer experience. Other issues that VoLTE faces are things like implementing call waiting and call forwarding. These are some of the reasons we've had LTE networks available for years, but no VoLTE until now.
There are a ton of benefits that VoLTE brings with it, though. One of these is spectrum allocation. Wireless carriers are constantly hungry for more spectrum. This pain can be alleviated with VoLTE. NTT Docomo in Japan reports that their spectrum usage is three times more efficient than their 3G circuit-switched voice service. That means carriers will be able to maximize the spectrum they already have, allowing them to add more customers and provide better services to existing customers. Carriers can also reduce costs by switching to VoLTE and retiring their 2G and eventually 3G networks. NTT Docomo retired their 2G network in March of 2012. Carriers in the U.S. still have active 2G networks but have plans to shut them down in the next 5-10 years.
HD voice and simultaneous voice and data connections are two other areas where consumers will benefit as we move to VoLTE. T-Mobile and AT&T already have HD voice active in several cities. Verizon plans to have it rolled out over their entire network by the end of the year. Another major advantage is the integration of VoLTE with Voice over WiFi. The setup needed for VoWiFi is essentially the same setup for VoLTE. Carriers will be able to offer better access to WiFi calling once they have VoLTE in place. Bring it on!