Hi -
The MWI On and Off numbers can be internal numbers that are valid within your CallManager dialing plan. For example, we use 1000001 for MWI On extension and 1000000 for MWI Off. These numbers are coded in CallManager and must jive with what you define within the Telephony Integration Manager in Unity. Note, if you make a change in UTIM, it requires a Restart of Unity, so plan for this after hours. To test, you should be able to dial the MWI On extension on your IP phone and it will turn on the light. Same for dialing the MWI Off extension - it should turn the light off. You can validate what CCM and Unity thinks the light status should be - in CCM you click on the hyperlink to the phone. In Unity, you click on the Messages link in the Unity SA for a subscriber.
Ginger