If you are asking how agents check voicemail, they dial 8500. It's in the Vicidial Manager's Manual. Note that their login password must be numeric (no alphabetical characters) so they can enter it on their phone to get into their VM.
If you are asking about configuration ... there are two basic ways to set them up: 1) in their "Admin->Phones" you can assign them a vm box number. 2) Create one in Admin->Voicemail (unrelated to their phone this way).
If you're asking something else ... I got no idea.