How do I retrieve my voicemail number on my cellphone?

I know next to nothing about cellphones, and I changed my huge voicemail number to 555 thinking I could then dial that quickly instead of searching through slow loading, ugly menus. I didn't really know that the phone actually *called* this number, so now I'm screwed. Can I somehow get it back?How do I retrieve my voicemail number on my cellphone?call your own number and press # when you get the voicemail message is the default almost everywhere