[Serusers] Call Forwarding Using PSTN Gateway

Newbie to SER. I am a little confused about how much I have to set up in databases to get an incoming SIP call to call forward to a PSTN number through SER. I have setup the username, attribute and value for my number, "callfwd", sip:1234567890@gateway.com in usr_preferences and the username in the subscriber file , added gateway ip to trusted, but call is immediately dropped when it arrives at SER. I have been through the getting started and have had success in modifying the values in the scripts, but don't see what data must be added into MySQL. Getting pointed in the right direction would be greatly appreciated Thanx murray