asterisk users - Aug 2004 - Can Zap detect line is already off-hook?

I have the need for a slightly odd * configuration for testing purposes. I
have a working * setup with SIP softphones, VoIP trunks and a single X100P
clone for PSTN access.

The PSTN line I'm using for testing is also in use by other folks. For
incoming calls, I'd like to set is up so that * functions as a voicemail
backstop on this line. This much is working fine.

For outgoing, I'd like * to be able to tell if the line is already in use by
someone else - ie when it tries to take the line off hook, can it detect
that the line is already off hook and return to the dialplan that the line
is unavailable?

--
David Gurr
Congruity Ltd.
Hemel Hempstead, UK