Caling people via Alexa who are stored normally on your normal mobile, from the contacts - can it be done (UK)?

From Amazon's page:
Alexa can make calls on the following compatible Echo devices:
• Amazon Echo (1st Generation)
• Echo (2nd Generation)
• Amazon Echo Dot (2nd Generation)
• Echo Show
• Echo Plus
You can also use the Alexa app for Alexa-to-Alexa Calling. This gives you the ability to make and receive calls between anyone from your phone's contacts list who has the Alexa app or a compatible Echo device, and who has also signed up for Alexa Calling and Messaging.

So you should be able to call his mobile from your Alexa if he has the app,installed in his phone and has signed up for calling and messaging. Note though that you cannot currently do this from a Sonos One (as it says, Echo devices only)

Echo's do work with Sonos. You will need to enable the Sonos skill on the echo device. Once set up (and there is a walk through on here how to do that, along with plenty of pointers from people who have had issues along the way) you can use the echo to 'control' Sonos. It is limited tho at this time, for example you cannot group by voice nor initiate playback from your local library by voice (you can control volume, next track etc tho once you start playback in the app). You can though initiate playback from Spotify and/or Amazon music. Again there are helpful hints on the boards from people that have had issues during setup etc. Hope this helps.
More info here:
https://en.community.sonos.com/amazon-alexa-and-sonos-229102/new-to-sonos-or-alexa-how-to-set-up-6791327

Regarding music play back, I subscribe to Apple Music but not Spotify. However when I tell my Dot with a simple command to to play music, it starts playing my iTunes music library. I can only guess that it’s obtaining this from my music library stored on my WD My Book which is wired to my router.
Shame I can’t ask for a specific track but if I do, Alexa tells me I don’t have a Spotify Premium account so it can’t play it!

There is currently no way for Alexa to initiate playback from Apple Music, be that streaming or your ITunes library. The two systems just don't talk to one another. What it could be doing is playing either music from Amazon Prime (free) or from your Amazon Music Library which often contains music you have bought on CD - Amazon often add MP3 automatically to your library for free.

From the info on Sonos support pages:
The following services are currently supported:
•Amazon Music
•Spotify
•TuneIn Radio
•Pandora (Not available in the UK)
•iHeartRadio (Not available in the UK)
•SiriusXM (Not available in the UK)

If you have an echo dot that is working, you obviously have an Amazon account, which automatically means you have an Amazon Music account (non subscription). If you have ever bought a CD from Amazon chances are that at least some of those will be MP3 in your Amazon Music library. You can check this out by logging into your Amazon account, holding your mouse over 'Your Account' and clicking 'Your Music'. I am not a Prime member or Amazon Music subscriber but I have 92 albums in there from purchases I have made over many years. And I can initiate playbcak via voice for the albums in there.
There is no way currently for the eco dot to play music from a local library (iTunes or otherwise) or stream from Apple music. If you can, please share with the community your setup as there are plenty of others on these boards that would very much like to play music locally stored via voice - myself included.