STOP IT NOW. BEFORE YOU DO MY HEAD IN.
The Voicemail Email settings in the IP Office configuration are nothing to do with IMS. [Anyone even thinking IMS Lite should be shot].
If you install IMS and don't install the IMS client on user do you really expect it to work!
If you have installed IMS and have given the users the IMS Client, and really really have a reason to want to also send them the wav file, look in the Voicemail Pro servers Control Panael for IP Office Voicemail Pro. Open it and uder the Email Settings tab you'll find options for Transmit Wav File and whether to Embed or Attach. ps. You don't have to do this for IMS to work just fine as Morrack explain.
NOW LETS ALL CHANT:- VOICEMAIL EMAIL IS NOT IMS, IMS IS NOT VOICEMAIL EMAIL.
[For the history buffs, Voicemail Email is a old Network Alchemy features (which begat IP Office). IMS is an old SDX feature, the guys who took over Network Alchemy, hence the confusing presence of two similar but different features.]
With that I'm going to take a holiday - beer and cider here I come.