asterisk users - Oct 2005 - Pattern for matching CALLERID

Hi,

I would like to use pattern matching in what some call the ex-girlfriend rule:

[demo]
exten => 830449/_0721.,1,Answer()
exten => 830449/_0721.,2,Dial(SIP/stefan,20,tr)

When I dial 830449, asterisk tells me:

Channel 'CAPI/ISDN1/830449-3' sent into invalid extension 's' in
context
'default', but no invalid handler

Could it be, that pattern matching doesn't work here ?
It want to route calls based on the prefix of the number, so if pattern 
matching doesn' t work, I would use SubString and GotoIf instead.

Have a nice day,

Stefan