you need to configure a dial-peer for the incoming call that "dials" the vm port configured in call manager. you also need a voip dial-peer that points the "dialed" number to the call manager.
example:
voice-port 3/0/1
connection plar 8800
description incoming call to voice mail where 8800 is the voice mail port in call manager
dial-peer voice 8800 voip
description main #'s to voice mail
destination-pattern 8800
session target ipv4:10.10.10.10
dtmf-relay h245-alphanumeric
codec g711ulaw
ip qos dscp cs5 media
no vad