Comment by wolvoleo

It was an optional part but without VoLTE you just could not call with 4G. For that the phone just switched back to 2G/3G.

That's not a sustainable solution because 2G/3G are getting switched off. And it doesn't really have any bearing on LTe itself.

The real issue is that they didn't really standardise VoLTE enough. Leaving every carrier and manufacturer to have a mesh of different options and not every carrier and every phone supports the exact same subset of options, which causes the compatibility issue. Also sometimes providers don't bother checking phones they don't sell.

They really should have standardised it 100% so this couldn't happen.