Hello, we have the following setup in our "Unified Messaging lab": SUAs <-> LAN <-> SER <-> Softswitch <-> PSTN The SER is provisioned as a SIP Server (essentially a SUA) from the Softswich point of view. We have provisioned a number block of 20 numbers (from a 30-channel ISDN PRI) for direct inward dialling (DID) to the SER. E.g. 12345620-12345639 are routed to the SER. On the SER we have a number of users &lt;user&gt;(a)dai-labor.debor.de, where the first 20 users have an alias of 123456[23][0-9] Each user also has his number added to his permanent contacts to enable (on the cheap) a "call by PSTN if not online" poliy. The aim obviously being to have a 1-1 mapping between URI and allocated telephone number (we are still in the proof-of-concept phase and will move to DNS and ENUM based architecture at a later stage). Scenario 1: OK PSTN user Up calls 12345621 - which is mapped to harry(a)dai-labor.de. If harry(a)dai-labor.de is registered, his SIP UA rings and the call is established. Scenario 2: problem harry(a)dai-labor.de wants to use his UA to place a call through the Softswitch. The Softswitch "authenticates" (if you can call this authentication ;-( by looking at the Contact header and comparing it to its database of numbers assigned to provisioned SIP Servers. I therefore need to be able to specify a rewrite of the Contact header to replace harry@<Contact IP:port> with 12345621@<Contact IP:port> when the callee is of the form <number>@<whatever> I am aware that this would be strictly speaking not proxy but rather B2BUA behaviour, but would still be interested to know whether anyone has a solution to this problem or whether we need to hack one ourselves. Many thanks in advance, Harry Dr. Harry Behrens Projektleitung BIB3R DAI Labor - Technische Universität Berlin Sekretariat GOR 1-1, Franklinstrasse 28/29, 10587 Berlin Fon: +49 30 314 23383 Fax: +49 30 314 21799 Email: harry.behrens(a)dai-labor.de http://www.dai-labor.de