3UK still have an agreement with Orange to provide the 2G signal, but only in areas where it believes it's own 3G signal is weak or non-existent.
So in major cities you would expect to only pick up 3's 3G, out in the country there'll still be access to Orange's 2G service.
This decision really only affects users who have a non-3G capable phone which aren't sold or supported by 3 anyway, so they're well within their rights to cut these folk off.
SV