Let me point you in the direction of EE which kinda of disagrees with your point:
To use 4G Calling you'll need:
- to be in an area with EE 4G coverage
- an EE pay monthly plan on one of these phones bought from any retailer*, including EE:
- Apple iPhone 6, 6 Plus, 6S, 6S Plus, SE, 7, 7 Plus, 8, 8 Plus, X
- Google Pixel, Pixel XL, Pixel 2, Pixel 2 XL
- Sony Xperia XZ1, Xperia XZ1 Compact
- Huawei P10, P10 lite, P10 Plus, P Smart
- Blackberry Priv, Dtek 50, Dtek 60, KEYone
- or one of these phones, bought directly from EE in-store, online or over the phone:
- Samsung Galaxy S9, S9+, S8, S8+, S7, S7 edge, S6, S6 edge, S6 edge+, Xcover 4, A3 (2017), A5 (2017), J5 (2017), Note 8
- Sony Xperia L1, XA1, XZ, XZ Premium, X, XA, X Compact, Z5, Z5 Premium and Z5 Compact
- Microsoft Lumia 550, 650, 950, 950XL
- Huawei P8 lite (2017), P9
- LG G6, G5, G5 SE, X Cam, K8 (2016), K8 (2017), K10 (2017)
- the latest software version on your phone – to update:
- iOS: Settings > General > Software Update
- Android: Settings > About Device > Software update (the exact software update menu option may be a little different depending on the type of phone)
- Windows: Settings > Update & security > Phone update > Check for Updates
https://ee.co.uk/help/help-new/gett...tures/how-do-i-use-4g-calling#article-title-2
As you can see if I wanted to buy the Huawei P8 lite for example I am restricted to buying it from EE directly as well as needing to be on a contract with EE which is what I was saying.
The only operator who allows PAYG customers to use VoLTE is Three as they offer the Three in Touch app which is clunky to say the least, I used to be with Three but left as their signal wasn't that great as they used to explain the poor signal as 1. But the 4G mast is too far away (A 10 to 15 minute walk if that) or 2. But there's is not enough capacity to provide a decent signal which is why I left.
I would love to be with a operator where I can use VoLTE natively without using any extra apps to do so but that is as likely as Virgin Mobile suddenly offering 4G to PAYG customers.
Anyway back to train wifi, I found the XC login page to be quick once and painless but I still like to know what networks are providing the wifi on board the UK trains.