Setting up Server to Server over the internet

I currently have 2 Asterisk servers one in California and one in Washington.
AsteriskNOW 1.5

My question is, or if I could be pointed in the direction.
How do I set them up to work together?

You could start here:
There’s also a good e-book found here (PiaF would do - this is a function of FreePBX) (Search for IAX)