A lot of technologies are adopted by 80 or 90% quite quickly after an initial slow adoption period and the it takes the other 10-20% a long time or they never do. This applies to mobiles, broadband and in some cases electricity, inside toilets, all sorts of things.
Digital exclusion is a big problem and will be in future, just I don't know how you solve it. Marginalised groups are often time rich and cash poor.
I agree re issues of electricity or outside toilets
(Our house, in a middle class area of inner London, did not get electricity until the early 1960's and next door only installed an inside toilet and bathroom last year!)
I googled "digital exclusion"
Interesting, it affects around 15% of the UK population.
http://heatmap.thetechpartnership.com/
In summary they have identified 4 main kinds of challenge that people face to going online:
- access - the ability to actually go online and connect to the internet
- skills - to be able to use the internet
- motivation - knowing the reasons why using the internet is a good thing
- trust - a fear of crime, or not knowing where to start to go online
Digital inclusion is about overcoming all of these challenges, not just one.
The OP phone number issue would also be covered by some of the above.