The problem with your description of your scenario is that it is not technically accurate. Conceptually, you may think that Freeswitch merely "acts as a media server" and "all SIP signalling is proxied through Kamailio", but in reality, all SIP signalling passes through FS, too, which generates a new call leg in the process, as it's a B2BUA. Viewed in that light, the question isn't so much whether you can "relay" a 407 challenge (you cannot) as whether you can obtain valid credentials from the caller and feed them as a response on your outgoing leg. -- Alex Balashov | Principal | Evariste Systems LLC 1447 Peachtree Street NE, Suite 700 Atlanta, GA 30309 United States Tel: +1-800-250-5920 (toll-free) / +1-678-954-0671 (direct) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/ Sent from my BlackBerry.