How do i change my voicemailbox number?

I added another mobile as my preset voicemail number so when i get a new message it calls someone instead of 901 .im looking for how to change the number back.How do i change my voicemailbox number?hi shaun, try ringing the voicemail number and listen to the options that it gives you on setting up a voicemail connection from another phoneHow do i change my voicemailbox number?die@