This is almost 100% of the time the result of a stuck VMPro assisted transfer action and is to be resolved in VMP 3.0(19). The CQ associated with this is:
CQ 24554 "Assisted Transfer calls fail to disconnect from VoiceMail Pro if hung up on before being answered"
Kyle Holladay
Certified: ACACN, ACSCI, ACSCM, TIA-CTP
"If it worked the way it should you wouldn't need me