After much testing and trying to work out whats the cause of my problem i’ve ended up here.
The problem in which i am having is :
8x Cisco 7911 all flashed with SIP firmware
They work fine locally on the same local network, when i use away from the office they do not want to connect.
I have two draytek routers linked to the two sites via lan to lan, i know this is working as i’ve got a cisco 7940G working fine.