asterisk users - Feb 2006 - Busy signalling for mobile callers ?

Hi folks,

Got an oddity that a user has raised to do with busy signalling and 
inparticular when calling from a mobile phone. It seems that the 
behaviour when calling * is slightly different to the norm i.e. If I 
call an engaged landline number directly from my mobile then the mobile 
gives engaged tone plus displays "number busy" then hangs up. If
however
I call * and pass the call simply to "Busy" then I get either the 
regular engaged tones (priindication=inband) or three short tones 
followed by hangup (priindication=outofband). I thought this might be 
down to iSDN being in the path but I have tried a similar test using a 
PBX on an iSDN 30 and that seems to act normally.

Can anyone verify this behavour and tell me if it is normal or bug worthy ?

This is tested on asterisk 1.2.1, caller and callee in UK.

Tristan.