BT Business Broadband Voice and Outboundproxy Problem

I am trying to get BT Business Broadband Voice working with asterisk and freepbx and have come accross the following problem.

The service uses an outbound proxy. In my case the registrar bmnha-01.bt.com is not resoveable by DNS.

The outbound proxy is www.bbvservice-560129.bt.com:5060

If I set the trunk the way the way I believe it should be configured, it does not work. I immediately get an all circuits are busy and there appears to be no sip activity.

If I then replace bmnha-01.bt.com with sipgate.co.uk and reload, I correctly get sip traffic to the proxy but of course it fails.

If I now put the original bmnha-01.bt.com back in as the host and reload, everything works perfectly as it should.

I should add that I have also tried a random string as the hostname eg hfjgktu.com and again there is no sip traffic, its almost as if I need to reload after entering a publicly resoveable DNS name to "kickstart" it first. None of this survives a restart.

my trunk config is:

username=0560129xxxx
type=peer
secret=XXXXXXXXXXXXXXX
qualify=yes
nat=no
insecure=very
outboundproxy=www.bbvservice-560129.bt.com:5060
host=bmnha-01.bt.com
fromuser=0560129XXXX
fromdomain=bmnha-01.bt.com
dtmfmode=rfc2833
disallow=all
context=from-trunk
canreinvite=yes
authuser=0560129XXXX
allow=g729&ulaw&alaw

Has anyone come across this?

I'm using asterisk 1.6 and freepbx 2.5.1.

TIA

PARTIALLY SOLVED

I added an entry in the hosts file for bmnha-01.bt.com with the IP address of the proxy server. This starts sip traffic flowing.

I still have another outstanding problem which I will nail though