[Users] help: anonymous call

Below is the anonymous call invite method compared with the normal call. In the from header, there is missing username. How can I add an anonymous username (i.e. <sip:anonymous@203.193.46.4>) in the from header if the call is from anonymous? Invite method from Anonymous call ---------------------------------------------- U 203.193.46.4:54169 -> 203.193.46.6:5060 INVITE sip:36428473@203.193.46.6:5060 SIP/2.0. Via: SIP/2.0/UDP 203.193.46.4:5060. From: <sip:203.193.46.4>;tag=1924AB7C-EE5. <----------------------------- missing username To: <sip:36428473@203.193.46.6>. Date: Wed, 28 Dec 2005 09:22:19 GMT. Invite method from normal call ---------------------------------------------- U 203.193.46.4:50197 -> 203.193.46.6:5060 INVITE sip:36428473@203.193.46.6:5060 SIP/2.0. Via: SIP/2.0/UDP 203.193.46.4:5060. From: <sip:34263634@203.193.46.4>;tag=978CF54-291. To: <sip:36428473@203.193.46.6>. Date: Fri, 23 Dec 2005 06:29:08 GMT.