Say good-bye to the PDA.

The PDA – short for Personal Digital Assistant and popularized by the Palm Pilot in the early ’90s – is fading fast from its once vaulted place as the digital doorway to organizing our schedules, calendars and contacts.

It’s been replaced by the smart phone, an all-in-one device that does all that the PDA offers and much more – like making telephone calls, surfing the Internet, sending and receiving instant messages and e-mail, taking pictures and video and playing music.

And now even the Palm operating system (Palm OS) that started the whole trend is about to go the way of the floppy disk, replaced by a system from archrival Microsoft.

Palm announced last week that it would use a mobile operating system from Microsoft to power a new line of Palm Treo smart phones early next year.

Ultimately, it means Microsoft is going to get bigger and more ubiquitous and that consumer choice is going to be limited.

The next-generation Treo, dubbed the 700, will run on the Windows Mobile operating system, a sort of miniaturized version of the familiar Windows program that we have on our computers.

And you’ll be able to use it as a phone and go online through the Verizon high-speed wireless network.

“We’ve long believed that the future of personal computing is mobile computing, and our collaboration with Microsoft is a historic step in delivering that vision to a larger market,” said Palm chief executive Ed Colligan in announcing that it was adopting the operating system of its former chief competitor.

Why the switch?

Because, said Colligan in what amounted to a throwing-in-the-towel concession, Microsoft is better.

“This is about growth and new functionalities that we believe the Palm OS doesn’t have,” he said.

Colligan says Palm still will make devices that use the Palm operating system. But don’t expect that to last for very long. The company spun off its software arm, PalmSource, in 2003 but continued to be its main customer. Earlier this year, PalmSource was sold to a Japanese company and now, with the alliance of its once parent company to its chief rival, PalmSource’s future has to be considered tenuous.

Microsoft has won another computer war, just as it did with desktop computers and Web browsers.

Earlier this year, its Windows Mobile platform suddenly and dramatically replaced PalmSource as the leading platform for hand-held devices. A year ago, Palm’s OS ran 42 percent of all the PDAs, compared to Microsoft’s 37 percent share, according to the tech research firm Gartner.

This summer, Microsoft exploded its market share to almost 46 percent while Palm dropped to less than 19 percent.

That leaves just one major smartphone rival for Microsoft: Research In Motion Ltd., the maker of the BlackBerry.

The BlackBerry is first and foremost an e-mail machine, running on its own proprietary operating system. But it also has pretty good calendar and contact features, Web surfing capabilities and, of course, mobile phone functions. There are more than 3.1 million BlackBerry users across the United States.

Microsoft and Palm’s Treo smartphone especially will be targeting business users.

“We’ll make sure it’s a big, big hit,” Microsoft Chairman Bill Gates said at the news conference.

Research In Motion signaled last week that it was not going to sit still. A day after Microsoft’s news conference, it announced a new partnership with Intel to produce next-generation BlackBerries that run on faster wireless networks and offer new features.

As the PDA dies and Palm is conquered, the battle moves to the smartphone field and RIM has to know its BlackBerry is in the crosshairs of a behemoth.