Verizon on Tuesday shared more details about its upcoming voice over LTE (VoLTE) service.

Called 'Advanced Calling 1.0', it will enable customers to place high-definition voice and video calls from their handset's native dialler, provided they own a compatible device. Contacts who are able to receive video calls will display a camera icon next to their name in the phone's address book. Customers will also be able to switch between voice and video calling without hanging up.

"HD voice and video calling only work when both people are in the Verizon 4G LTE coverage area and are using VoLTE-enabled smartphones from Verizon," said Debi Lewis, a director of Verizon Wireless' corporate comms team, in an article on the U.S. operator's Website.

Verizon unveiled its nationwide VoLTE plans in May. It did not provide a launch date but said it aimed to roll out the technology by the end of the year. It also did not say which handsets would support VoLTE, only that it would offer "a robust line-up" of compatible devices.

Fast-forward to Tuesday and the picture remains more or less the same.

Verizon said it will roll out VoLTE "over the coming weeks" but did not provide a more specific timetable. The official Advanced Calling 1.0 Website merely states that it is "coming soon". Verizon also reiterated that "a number of devices" will be able to use VoLTE courtesy of a software update but did not disclose which ones.

Verizon is fairly late to the VoLTE party in the U.S.

T-Mobile US launched it in select markets in May, quickly followed by Verizon's closest rival AT&T.

Meanwhile, Sprint has said it is working on VoLTE but has yet to confirm when it will launch.