Why VoLTE? Superior call quality, almost instant ringing, better battery life, and simultaneous voice and data over LTE. Verizon finally gets simulatelous voice and data for the first time. It didn't happen with the 4, 4s, 5, or 5s. For some reason, theres no form of software update that can enable VoLTE on those devices and it only works on the newer Iphones. It took them 4 years worth of Iphones to finally get voice and data. It's not perfect yet, if you have a weak LTE signal that likes to switch between 3G and LTE, you will be in dropped call hell. Sprint has HD Voice over it's 3g network. The 5s, 5c, and newer Iphones support it. They are the ONLY carrier now that can't do simultaneous voice and data, and we are in late 2014. Their LTE network is also far behind the other carriers. Going to leave AT&T out of this one as their VoLTE is not nationwide yet and is only available in a few areas..they are lagging in the game so far. T-mobile is by far the most advanced when it comes to VoLTE on Iphones, but their LTE network is still hard to compare with the likes of AT&T or Verizon, although there has been huge improvement to it lately. They are the most advanced so far is because You can make a call on LTE, and if you drop the signal and go down to 4G, your call won't drop like Verizon.