asterisk users - Feb 2006 - using AMP custom extensions

Hi all, I'm trying to setup a custom extension in AMP (yes i can code it 
by hand but the on-site admin that does moves & changes cannot).

I've tried the following

 > add cutom extension

600

in the dial box i have

Dial(IAX2/username:password@host/$EXTEN@from-internal)

this doesnt work as these lines are added to extensions_additional.conf

exten => 600,1,Macro(exten-vm,novm,600)
exten => 600,hint,Dial(IAX2/username:password@host/$EXTEN@from-internal)

anyone know why the hint line is there?

does anyone have custom IAX extensions configured thru AMP?

Thanks in advance

Bails