asterisk users - Mar 2005 - ringing CAPI & SIP channels together

Hello,

I have an asterisk box with ISDN (CAPI) phones (using chan_capi that has 
them as Zap channels) and SIP phones connected to it. I want to have a 
extension that rings 1 CAPI and 2 SIP phones together as a group.

I tried the following but when either the capi phone either one SIP 
phone is busy, asterisk goes directly to the BUSY extension.

Any idea how to overcome this ?

Thank you in advance,
Dimitris

exten => s,1,Dial(Zap/g5/111694&SIP/g4,20,Ttwr)
exten => s,2,Goto(s-${DIALSTATUS},1)
exten => s-NOANSWER,1,Voicemail(su111694)
exten => s-NOANSWER,2,Hangup               
exten => s-BUSY,1,Voicemail(sb111694) 
exten => s-BUSY,2,Hangup                  
exten => s-CHANUNAVAIL,1,Playtones(dial)
exten => s-CHANUNAVAIL,2,Hangup
exten => s-CONGESTION,1,Playtones(congestion)
exten => s-CONGESTION,2,Hangup
exten => _s-.,1,Goto(s-NOANSWER,1)
exten => a,1,VoicemailMain(111694)  
exten => i,1,Playback(invalid)
exten => i,2,Hangup
exten => t,1,Hangup