[Asterisk-Users] Help with extensions

[Steve Blair]

Hello:

   I'd like some help with defining extension rules. I want calls arriving
at Asterisk from my SIP proxy to be sent directly to voicemail. I'd
also like the appropriate greeting played when the call gets to
voicemail.
 
   My proxy prefixes the extension with a "u" or "b" based on
SIP response codes before relaying to Asterisk. So when the
call arrives it is in the format [u|b][3|6|7|8]<four more digits>

   If I hard code the following rules then calls get forwarded
as expected.
     exten => u67501,1,VoiceMail2(${EXTEN})
     exten => #,2,Hangup

   However to save on typing I'd like a general rule. I've tried
the following but Asterisk cannot find the extension with this
set of rules. Can someone explain how what I want can be
accomplished?

    exten => _[ub][3678].,2,VoiceMail2(${EXTEN})
    exten => #,2,Hangup

Thanks