Thanks - however to get to the DMZ, traffic still has to cross the router :-)

Its currently in the DMZ, and I spent some time this afternoon trying different firmware - 8.2, 8.8, 8.9 and 8.12 . Im still without inbound calling. Im going to reconfig the network and stick the phones on their own VLAN (so take them out of the DMZ) and route direct - ill see if that makes a difference.