Apple appears to working towards VoLTE support on the iPad, but it's not yet clear when that capability might be added to commercially available products.
Apple Inc. (Nasdaq: AAPL) is expected to introduce the latest version of its iPad later this week (October 16), hot on the heels of the launch of the iPhone 6, which heralded Apple's first support for voice-over-LTE capabilities. (See Apple Eyes VoLTE as 4G Voice Gets Real.)
It seems clear that Apple intends to add VoLTE support for the iPad too -- at some point. A job posting from September, for instance, calls for a cellular engineer with VoLTE experience to work on the latest wireless features for the iPad and iPhone. It is also looking for engineers with SIP familiarity for Facetime and VoIP updates for iOS. (See Analyzing Apple & VoLTE.)
VoLTE works by using the Session Initiation Protocol (SIP) to initiate the 4G calls, which are transmitted in data packets, with the IP Multimedia Subsystem (IMS) in the core network controlling the call session.
There is already a thriving ecosystem of third-party SIP clients that turn the iPad into a VoIP phone.
Apple could update the telephony stack for the iPad to allow VoLTE support now that it has introduced the feature with the iPhone 6. In theory, this could eventually allow VoLTE voice and video calls between different carrier networks and iOS and Android devices.
In practice, though, that won't be the case for a while: Even though Apple timed its support for VoLTE just as the major US mobile carriers began adding true 4G voice capabilities to their networks, most users don't have a VoLTE-compatible device. And while the carriers are now working on VoLTE interoperability between their networks, there's no indication yet as to when that might become a reality.(See Apple's New iPhones Have 20 LTE Bands, VoLTE and AT&T's Rinne: Carriers Working on VoLTE Interoperability.)
— Dan Jones, Mobile Editor, Light Reading