Joined: Jan 14, 2003
Posts: > 500
I see the main global problem and it's lack of VoLTE roaming. When 2G and 3G are shut down you can't use your mobile phone abroad for calling. Yes, you can roam in 4G and use all kinds of apps for internet-based calling, but you will be out from usual mobile connection for calls.
2G roaming and 3G roaming are easy and elementary: if two operators have roaming and your phone supports 2G/3G frequencies, you are fully connected: talk, sms and often also data. You can call and you can be called.
In 4G roaming you can use only data. I don't understand why 4G was first created without a call option. So the VoLTE had to be invented afterwards.
VoLTE roaming is such a new option that it's impossible to rely on it while travelling in the world.