First spotted by Lightreading, Apple is looking for a Cellular System Protocol Engineer and Senior Baseband Audio Engineer, with both jobs listings asking for experience with VoLTE.
3+ years of hands-on experience with wireless technologies (WCDMA, CDMA, LTE, VoLTE, IMS), systems architecture, protocols, and standards is desired.
Major US Carriers like Verizon, AT&T and T-Mobile have all announced their VoLTE rollout plans.
Current iPhones do not support VoLTE, however chipsets in the iPhone 5s/5c/5 could support VoLTE if Apple were to release a software update to enable it. Previous reports hinted that iOS 8 would enable VoLTE for those iPhone models, but that has currently not been the case. Apple could always add features in the GM release, such as VoLTE, or even enable it when it launches the iPhone 6.