According to this document http://wiki.3cx.com/documentation/networking/sip-proxy-manager , Aastra phones do not work with the 3CX Tunnel Proxy. The document seemed a bit old and I wondered if that is still the case with the current Aastra firmware and 3CX v8?
"Known Limitations
Currently the Tunnel Protocol included with the SIP Proxy Manager cannot be used with Aastra phones since Aastra uses SIP headers which the current Tunnel does not handle. There is no known workaround for this limitation.
"
"Known Limitations
Currently the Tunnel Protocol included with the SIP Proxy Manager cannot be used with Aastra phones since Aastra uses SIP headers which the current Tunnel does not handle. There is no known workaround for this limitation.
"
