Hide a phone number

I want to store a contact that dials into my work Voice mail system, then dials my extension, then enters my password. For obvious security reasons, I would like the entire number string to only be viewable if I am editing the contact, but I don't want it to be viewable when I dial or when viewing my calls log. Is there some way that you can mask an entry so it isn't viewable (like showing asterisks when entering a password on a computer)?