extensions.conf

[localphones]
exten => _X.,1,Dial(CAPI/ISDN1/${EXTEN}/b)
exten => _X.,n,Hangup

exten => 555,1,Answer()
exten => 555,n,Playback(tt-monkeys)

exten => 14,1,Answer()
exten => 14,n,Dial(CAPI/ISDN1/555-14/b)

exten => ekiga,1,Answer()
exten => ekiga,n,Dial(SIP/ekiga)

[directdial]
exten => 1,1,Dial(CAPI/ISDN1/${customernum}/b)