Hi Isidoros,
If you are looking to turn the MWI Lamp off on a particular phone;
Give this a try.
To find the MWI - OFF DN (just in case
In CUCM look up the MW-Off number (Feature>Voicemail>Message Waiting>Directory Number>Message Waiting Indicator Off )
This will be a Directory Number like perhaps 2600. Go to the phone, press the Line button, dial 2600 and the MWI Lamp/Icon and Message will turn off.
If you are looking to set up a phone/phones where the MWI lamp does not turn on when the user
has new Voicemail;
Find the phone in CUCM/Admin go to DN config page> Message Waiting Lamp Policy> set to NONE
This will set the phone to not light the MWI Lamp or Icon indicator when new messages are received
Cheers!
Rob