We nay have to wait a considerable time, remember Google Voice NEVER came to UK! UK and European telecoms industry is a bit of a hard nut. But of-course this is Amazon, I have better faith in them...
I don't see what the telecoms industry has to do with it as Alexa Messaging doesn't allow calls to regular landline phones. The only thing phone related is the linking it to your mobile number, which may need them to be able to send SMS messages in the UK for verification if that is how it works.
Echo-to-echo calls makes use of QoS mechanism over the internet (which comes via Telecoms companies, who may block or disable certain QoS demands on their networks).
In addition, in an ideal situation, we should be able to make calls to mobiles or landlines using echo, or send text messages. This is happening already in the US. There are even IFTTT recipes that connects Alexa and US phones. That's the capability I was mainly talking about.