One of the first social networks was the speed dial. Your way of friending someone was to put them on the speed dial list.
It was lots of closed networks, that is for sure.
Seinfeld had an episode on the importance of it.
This all went away with the advent of the addressbook. I thought it had died forever until I realised that it reared its head with the advent of the qwerty keyboard on a phone.
Instead of numbers, I now have speed dials for letters. H for home, etc.
If you have two friends with first names of J (Jim and Jon) what do you do? You can friend only one.
Why does it matter? It is still a nicer interface to hold down one character to call someone than to use the addressbook feature.