I now find that I'm unable to fully use the phone function - I've plugged my old land-line in and can receive calls to it, but not make them. After some looking around online I get the impression that there are some VoLTE settings which are disabled in my firmware, so I'm looking to unlock them and I wondered if this firmware would do the trick.
I also have a 525 branded three.ie. I find that as long there is a good 3G signal I can use the telephone. The settings must be on automatic but you can use the LTE inspecteur to select the bands you wish to use to get the best results. It does not always return to these bands when the call terminates. Sometimes you'll have to reset to your chosen settings.
I use mine in two different areas, one there is no coverage 3G or 4G going by the coverage map (right in the middle of a not spot) but get up 60mbps 4G+ (CA) down with 3 or smarty when using LTE inspecteur, sometimes the unit does select the best bands but mostly I have to force it.
I have to manually select 3G to attempt a telephone call as letting the unit do its stuff mostly does not work. Sometimes it does not work at all due to the lack of a 3G signal.
In the second area I use the 525 I get slightly better signals both on 3G and 4G (good coverage on the maps) and the telephone can be used without any manual selection of 3G, again for best results using LTE inspecteur to manage the bands - or the Polish app. In this area I do not get as high download speeds and no 4G+ has ever been noticed. Higher density of population and CA/4G+ not enabled perhaps.
Hope this helps a bit for users of the "Irish "Three 525.