2-Step Authentication using phone

When you are on the page to create the account, it tells you to enter "at least one" contact method.  So yes, you can use either a cell phone number, or an email address.  However, if the phone number is already connected to another account at the same service address, you won't  be able to use it again.  Same with an alternate email address.  And no, it can't be another Comcast address.