Heads up…. I got in this trap when transferring a facebook name from my personal account to a page.
I have had an account with the name http://facebook.com/colinlewissmith for some time. I decided I wanted that url associated with a page I have been playing with. I changed the name on the facebook account to something else ( http:\\facebook.com\colinlewissmithpersonal ), assuming I could then instantly assign facebook.com/colinlewissmith as the pagename to the page I have been playing with here : face book page
NO SUCH LUCK. When I try it change it to colinlewissmith it appears as “unavailable”.
Research tells me this is a common occurrence. It often takes weeks for facebook to release the old name after you make the change on your account.
I am now patiently checking availability every day.