Hi eatyourveg
I don't have any personal experience of this, my children are still very young, but I have asked someone else about it.
I don't know if it will be much help for you, it may be quite a different situation, but I know that my cousin (one autistic child, another older child left home) has found skype very useful. They have specific set routines, so they have a specific time every day to go on skype. (after dinner in the evening, she said) However, it is a bit different as they are living in Bristol and Bath, so not too far away and they can arrange frequent visits. And her older child is not at uni, he is working, but he is still elsewhere!
I asked my cousin how it was at the beginning, she said it was quite difficult at first. They arranged a new activity for the younger dc as a distraction technique, but it wasn't a good idea and it didn't work out well, perhaps it was too much along with the older boy going away, too much change in routine all at once.
She also said they have problems when the routine is broken because the older boy can't skype or whatever, but in the main it works well for them.
I don't know how helpful that is for you, I don't actually know my cousin's children well, as I only see them at the occasional family gathering when I am visiting the UK, and the younger one will not talk to me. I talk to my cousin on skype sometimes, though usually late in the evening and I don't see much of the children.
I hope it all works out for you.