asterisk users - Oct 2006 - FOP v.27 IAX trunks not "ringing"

I am using FOP .27 and I have Zap & IAX trunks. Although the IAX trunks 
do show and appear registered (not dimmed) on the display, they show no 
activity while in use. Any ideas??

Segments of op_buttons.cfg & iax.conf are included:

op_buttons.cfg
[Zap/1]
Position=23
Label="Cook (Main)%0a(905) xxx-xxxx"
Extension=-1
Icon=0

[IAX2/416xxxxxxx]
Position=24-26
Label="Personal Line%0a(416) xxx-xxxx"
Extension=-1
Icon=0

[IAX2/647yyyyyyy]
Position=27-28
Label="Business Line%0a(647) yyy-yyyy"
Extension=-1
Icon=0

iax.conf
; Registrations for remote IAX servers (dynamic config)
register => 416xxxxxxx:zzzz@iax01.unlimitel.ca   ; Personal
register => 647yyyyyyy:zzzz@iax01.unlimitel.ca   ; Business

[416xxxxxxx]
; Unlimitel DID - Personal
username=416xxxxxxx
type=user
context=DID-incoming


[647yyyyyyy]
; Unlimitel DID - Business
username=647yyyyyyy
type=user
context=DID-incoming

Thanks, dbc.