If you set your phones region to United States & reboot you’ll get live voicemail. I’ve had my phone like this since the beta and haven’t noticed any issues so far, you can set your metric and date preferences to UK etc
You can set your keyboard language to English UK, the only difference I’ve really noticed is that some of the items in settings are American for example “Cellular” menu instead of “Mobile data”
If you set Siri to Language English (US) you get voicemail transcriptions too, you can set the voice to British so again no real difference as far as I can tell.
What phone are you using, I've tried changing region and Siri to US and am still not even getting Live voicemail, let alone the transcribe feature. With an iPhone 14 Pro.