The first UK network to offer VoLTE has gone live with its voice-over-data service, with Three lighting up what it’s calling 4G Super-Voice. Kicking off today in London, Edinburgh, Exeter, and Birmingham – where Three says it has more than three quarters of the population covered – 4G Super-Voice also boasts better indoor calling performance.

That’s thanks to greater use of the low frequency 800MHz spectrum, which does better at reaching into buildings than the higher frequency spectrum. According to Three, around 50-percent of the UK population are now catered for with indoor coverage with 4G Super-Voice.
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https://www.slashgear.com/volte-goes-live-in-the-uk-but-not-for-your-iphone-yet-15404759/