NEVER press a number, No matter what the message prompts, It is a trap to bill your phone a collect call costing big bucks. use the 3 tone disconnected chime in Barberas comment place it before your message in your voicemail. The auto dialer will hear the tones hang up and remove your number.
If your phone allows it, use google voice, block the call as spam, then it gets a computer message that starts with 3 tones and then says the number has been disconnected. Your phone never rings and you don't lose minutes as google screens and blocks it for you.