By 2013, Verizon plans to deploy nation wide VoLTE in USA. Verizon is currently testing VoLTE in two cities. "We’re continuing to work on VoLTE and the services it brings, and will share any launch or availability plans in due course." said Verizon spokesperson. VoLTE is similar to VoIP where voice is caried over data networks. VZ's VoLTE network is based on "IP Multimedia Subsystem", an architectural framework to deliver IP multimedia serivces over LTE network. For more information on how this network works, read this article.