One of the things Comcast overlooked when setting it up. We have the same problem; only have cell phones and each is "already assigned to another account." Also no non-Comcast email address, and no need for one except for this. Unfortunately, there isn't anything we can do about it. Fortunately, you can click on "remind me later" (or something like that) in tiny text at the bottom of the page. That seems to make the reminder go away for a while.