PHP/5.5 is out . The SQLSRV driver currently available requires PHP 5.3.6 or PHP 5.4.
Additionally, there're now official binaries for x64 architecture  although they are tagged as "experimental". (Third-party binaries have been available for years but Microsoft policy is to only support the official ones.)
Update #1: PHP/5.6.0 alpha 1 is out .
Update #2: PHP/5.6.0 final is out .