ZuluAlpha and sarond are correct...
Your phones will register to the Master....
First, fix the site access. If ping doesn't even work, then it could mean the network isn't working as it's supposed to be.
You can do a ping test from the Master to an IP from the remote site via Telnet. if I am not wrong, in R4.1 or <R5, you can telnet to port 23 and do ping or dnsquery rfom there. At least you can also check that direction.