Australian relatives?

I've been conducting some research into a family related to mine, my mother's cousins, who went to Australia in 1948. (Via GenesReunited)
I've discovered that the two teenagers who I remember playing with, may well be still alive and I now have two addresses and phone numbers which may well be theirs!
Not quite definite though....
Now I feel really shy about contacting them and don't know which way to go. Do I phone? Do I write?

Email would be so much easier, but I don't have those addresses!
It's the first time this has happened in ten years of doing my family history.... any ideas?