phone and router compatabilty problems

I have a Thomson gateway 585v7, and a siemens c474ip dect phone, a sipgate.co.uk account, the phone keeps dropping the router and if you call at that point its just a dead line.
Sipgate recommended forwarding ports 5004, 5060 and 5062 and disabling the stun server. But this is proving to be quite difficult with this router, I have a fixed IP and am on adsl2+ .
Can anyone help or point me in the right direction.
Vince

I believe this link will give you an idea on how to port forward on that specific router.

http://forum.portforward.com/YaBB.cgi?num=1235285461

it's hard for me to give you direct steps as every router is different

Thanks, have joined that forum and can post in 24 hours, do you think I should disable upnp and re enable the stun server in the phone, I have seen some posts that say this.

Sipgate contacted me and said to try witout the port forwading. However it doesnt work, and I get an error code now. ip code 404.
Any ideas
Thanks

bump