Microsoft, the No. 1 software developer, is making a major push to get its new Windows 8 onto mobile platforms, including smartphones.

Microsoft CEO Steve Ballmer Monday announced new smartphones from AT&T will be compatible with the new software to be released later in 2012. Later, at the International Consumer Electronics Show in Las Vegas, he is expected to announce a major tie-up with Finland's mobile phone giant Nokia.

Ballmer made an unexpected visit to a developers forum sponsored by Dallas-based AT&T at the CES, where he promised Microsoft will support the full range of 4th generation long term evolution (LTE) smartphones for the carrier. AT&T is the second-largest U.S. mobile carrier.

Ballmer also said Redmond, Wash.-based Microsoft will have a Windows phone soon.

AT&T also unveiled a series of Android-based tablets from Sony, Samsung Electronics and other manufacturers at CES.

Later, Ballmer is expected to deliver a keynote address at the CES where Nokia CEO Steve Elop - a Microsoft senior VP until 2010 - is expected to join him. In the fourth quarter, Nokia introduced its Android-based Lumia phone to compete in the sector with Apple's iPhone series.

But Nokia is expected to announce it will deploy Windows 8 on tablets, cementing ties between the two companies. Such a deal might also squelch speculation about a takeover of ailing Research in Motion, the Canadian BlackBerry developer, whose 75 million customers run devices built in proprietary RIM OS.