my exchange was also tweeted, and shows as accepting orders on Open Reach Where and when map.
but not on Samknows.com, or any of the ~20 or so post codes i've tried for it via BT's checker.
can't say for your exchange, but i'm willing to bet i'll be able to order early next week, my Cabinet has been there for months, and has all the work required for it go live done
reason i mention samknows is, they get data from bt - if they can't see it's not available for some, bt/other isp's prob can't either