a few (mostly obscure extensions) can be purchased in the aftermarket - for example L.fo is currently being auctioned <a href="http://www.sedo.com/auction/auction_detail.php?language=e&auction_id=85745" rel="nofollow">http://www.sedo.com/auction/auction_detail.php?language=e...</a> - also see <a href="http://www.namepros.com/domains-for-sale-fixed-price/616074-largest-portfolio-single-letter-domain-names.html" rel="nofollow">http://www.namepros.com/domains-for-sale-fixed-price/616074-...</a>
wiki = friend<p><a href="http://en.wikipedia.org/wiki/Single-letter_second-level_domain" rel="nofollow">http://en.wikipedia.org/wiki/Single-letter_second-level_doma...</a><p>They're reserved by ICANN