First of all sorry for this post not being in the thread it belongs to (I've not the initial mail).

But, I don't want to use the Asterisk dtmf features, I want to use the SIP INVITE/REFER features from the UAC (actually polycom and snom phones).

Can someboy shed me some light on this?

You receive a call from Asterisk UAC and want to transfer (blind or attender) to other UACregistered in OpenSer.

Of course you don't need Asterisk native transfer, SIP allows blind and attended transfer. The only you need is that your SIP devices allow both of them (unfortunatelly many SIP devices just allow blind transfer, but in most cases reading the device manual you'll find how to do a attended transfer).

The point here is that Asterisk allows receiving a REFER, so don't worry for that (I use your same escenary with no problem and SIP transfers).

Maybe you find useful this links: http://tech-invite.com/Ti-sip-service-4.html http://tech-invite.com/Ti-sip-service-5.html http://dev.openwengo.com/trac/openwengo/trac.cgi/wiki/SipTransfer

Regards.