Hi,
This is possible, but does have some restrictions that may or may not be problematic for you.
Connection Trunk Design Considerations and Limitations
http://www.cisco.com/en/US/customer/tech/tk1077/technologies_configuration_example09186a00800afd65.shtml#contrunk_design
Connection Trunk mode is supported with these voice port combinations:
recEive and transMit (E & M) to E & M (same type)
FXO to Foreign Exchange Station (FXS)
FXS to FXS (with no signaling)
Note: These voice port combinations are permitted between analog to analog, digital to digital, and analog to digital interfaces. Also, when you are configuring FXS to FXS, signaling can not be conveyed because it would not be a transparent path. The connected devices (FXOs) would be trying to signal each other. It is possible to get this design to work if you set the voice path to always be open. Configure signal-type ext-signal to the VoIP dial peer, and the router will no longer wait for signaling before it opens the voice path.
signal-type ext-signal :
External signaling. The digital signal processor (DSP) does not generate any signaling frames. Use this option when there is an external signaling channel, for example, CCS, or when you need to have a permanent "dumb" voice pipe.
When you connect an FXS to another FXS, or if you have anything other than an FXS/FXO or E&M/E&M pair, the appropriate signaling type on Cisco 2600 and Cisco 3600 series routers is ext-signal (disabled).
HTH,
Bobby
