I'm having a similiar issue - I was going to try this - but haven't got a chance to try it yet
! The statement below enables H.323 to SIP translation
! in IOS so that H.323 calls to IP phones at this site can
! roll over to voice mail (SIP).
! in IOS so that H.323 calls to IP phones at this site can
! roll over to voice mail (SIP).
voice service voip
allow-connections h323 to sip
