Get your trunk from
https://www.tescointernetphone.com/account/?reset=true;
Then
Craete Iax Trunk
enter outbound Callid If you Like
Outgoing Settings
Trunk Name = Tesco
Peer Details
host=gateway.tescointernetphone.com
qualify=80
secret=s1n3ad
type=peer
username=01183320153
nat=yes
Incomming Settings
User Context = tesco number (eg 0118332X150)
User Details
context=from-pstn
type=user
Registration string
0118332X150:yourpassword@gateway.tescointernetphone.com
put your number and passwork the above wont work !
I changed qualify=60 to qualify=80 as i kept on getting (lagged) and it seems fine now i might try and put it back to 60 n see if you works any better.
Hope this helps someone