Voicemail is carrier-dsependent. They all do it differently, Call customer service, tell them you have a few questions about voicemail and they'll either walk you through everything or connect you to the department that handles voicemail. They probably get thousands of calls about voicemail every day,
As far as something other than 1 for voicemail, I can get it by calling my own number. With another carrier of mine, *86 was voicemail. Ask them.