I received a wishlisted book today that I was waiting for. I opened it up and the book looks unread! No crease on the spine,  and the pages are nice and tight! While checking through the book, I got to the last page and saw that someone had written two phone numbers (in ink) on the last page of the book!!! It's deep enough to be seen on the other side of the page.

Is there a way I can get rid of the numbers written there, without damaging the book even further? Like I said, this book looks new with that exception.

Since it's in ink, I don't think you can remove it without damaging the book.  I don't think it make the book unpostable unless it makes the text on the other side unreadable.  If you are worried about reposting the book-when you're ready you can offer it in the book bazaar or the genre thread and denote the problem with the phone numbers.  Then if someone wants it anyway, they'll know about the phone numbers beforehand.  

Okay thanks! I was hoping something would be able to get rid of the writing. But, I can live with it if I can't. :)

maybe some cover up tape (or correction tape could be used?

Hairspray will sometimes get ink out of clothing, but I wouldn't try it on a book.  The ink would probably bleed and make it worse.  Wish I could help!

Hairspray could cause 'liquid damage' and that would definately be unpostable.

If the ink (or indentation) is not on a text page the book is probably postable. 

Some ink is erasable.

You can try using a mild tape, like sctoch tape. and stick it to the page, then lightly pull it off. I have found that takes some stuff off, it might fade the ink on the page some though but it should certainly lessen the garish shades of that ink. You can also dab a 50/50 solution of bleach/water from a q-tip to the page. It should bleach the ink and the page pretty well. Just don't get everything wet! Hold the page up and dab... blow it to dry.... hhehe

Just as if it were in the beginning of the book, if the writing is not on the text of the book (not meaning pgs with text on them, meaning text of the story of the book) then in the back the same is true. If the numbers are not on the story TEXT pages of the book, then they aren't affecting it's postability at all. Post away!