The problem is that Freeswitch in its current incarnation insists that I send at least one DTMF digit out on the FXO port. I work around this issue by sending a ‘w’ “digit” as follows:

 

  <action application="bridge" data="freetdm/span_fxo_csd/1/w"/>

 

This does not actually cause any DTMF tones to be sent out on the FXO port (so my dialtone is not disturbed) but it does cause a 5-second wait before the dialtone is heard on the FXS port.

 

What I really need is this:

 

  <action application="bridge" data="freetdm/span_fxo_csd/1/"/>

 

Using this however results in the "No Digits to send" error.