We just replaced a old Siemens Hicom 300 system with a Callmanager 6.1.2 and a C3845 router with E1 (EURO-ISDN) as a H323 gateway.

Now the customer requires again the "Callback to CO" feature. The Siemens system was able to send callback requests to ISDN phones on the CO side (provider Austrian-Telekom).

The callmanager offers the Callback softkey button, but when pressed a message shows "Callback cannot be activated for nr.xxx". There is not even a messages sent to the router as the debug messages show.

I know, the callback was implemented for QSIG trunks only, but is there a way to get that working for standard euro-isdn lines, too?