When you start uni you will collect so many random mobile numbers, and the next day you'll only remember who half of them are.
If you're living in halls, my advice would be to go in self-catered flats. In traditional catered halls, you might meet loads of people at every mealtime, but it will take you ages to remember who is who. Here in my flat, from day one I've had five people who I know I live with, and we exchanged mobile numbers on the first day. Your flatmates effectively become your family, and are a good starting point for socialising.