If you have an MICS, you can run FLASH voicemail or CallPilot providing your MICS is new enough... I can't remember if the version you have is new enough..probably is though.
I wouldn't bother with a NAM if all you need is mail.
If it was me, I'd verify the version of MICS (again I think you are good) and get the CallPilot.
Fun fact: I helped design the IVR on CallPilot
