Thanks for help and explanation.Yes I know that I should use TLS. This was just a test.That's a pity, that this client is broken. I have just thought that I found nice and free sip client with srtp and tls support. I have found this client here: http://www.phonerlite.de/ , author Heiko Sommerfeldt. I hope, he corrects this bug.>The Polycom is the only phone that does this little tid bit correctly.Do I understand this correctly that there aren't any softphone clients that support SRTP via SDES correctly ? I found few clients that support SRTP here http://en.wikipedia.org/wiki/Comparison_of_VoIP_software but I haven't tested them yet.