how to unpack the IP datagram

   i want to control(deny or permit) the visiter to the wap gateway(wapbox),like a firewall.but i think i must know the mobile number of the user.in the kannel, as i know ,we can only get a dynamic IP address of the mobile ,so we can do nohting about the user, is there phone number in the datagram that the bearbox received and sended? if have ,we can unpack the datagram and store the phonenumber into a database like MYSQL .then check the phone number before the datagram been sent to the wapbox.
    thanks a lot