[Asterisk-Users] Cmd MusicOnHold works, but no sound when a call gets holded

[Christian Hiller]

Hello,

i have setup

exten => 555,1,MusicOnHold(default)

i can hear the music, so far so good.

But when i hold an incoming call by pressing the HOLD-key on my snom 
telephone - nothing happens.
No output at CLI  that the MOH gets played.
When debugging SIP on asterisk, in the moment i press the HOLD-key i can 
see some SIP-INVITE messages from the phones that holds the call to the 
other one.

Any ideas why its not working?

Christian