What do you say when you call someone without knowing their name?

First I think you should find out what his/hers name is before you call him/her. Because if you don't your conversation could be awakward, and it could lead to some nasty things, and you'll never get to really know the person. But if you still call them without knowig their name, start off with saying "Hey, it's (Your name), from school" (Or wherever you know them from) If their new to the place, ask them questions, start off by asking them what their name is. Then go from there with different questions, and them tell him/her some stuff about yourself!