i'd say msn was the saving grace for all my friendships... as well as texting. yeah you may go away and meet new friends, but seriously, i spend more time out of lectures that i do in them at uni, which means im generally either shopping, or sat in my room watching jeremy kyle and neighbours - in which case i'll be on msn. most people at uni tend to just leave it on all day long, so you can always get hold of someone even if they aren't there when you initially start the convo.
and as everyone else has said - you get so many holidays and they're so long at that, that you do have plenty of time to see your home friends.
i'm part of a group of 7 girls, and our relationship hasn't changed at all since we all went off. we still see each other just as often as we did, and i find that even if you are away for a long time, they're just so happy to see you when you get back, it doesn't matter on the time you missed out on, just catch up.