IBM Wednesday shook up its Web conferencing strategy adding a hosted option by acquiring WebDialogs and expanding its on-premise presence and conferencing platform Sametime.

The WebDialogs acquisition, for which terms were not announced, propels IBM into a market against Cisco and Microsoft, which also entered the market via acquisition. Cisco bought WebEx in March for $3.2 billion, and Microsoft acquired Placeware (now Live Meeting) in 2003 for $200 million.

The IBM announcement was made at the annual VoiceCon conference.

In addition to the head-on battle with the two giants, WebDialogs’s partnerships with Skype and Salesforce.com could prove fruitful for IBM, which could exploit them to integrate business tools and real-time communications, according to some observes.

“IBM needed to find someone with a hosted model, with some interesting partnerships, who would be attractive to the down stream market and who has some interesting reseller options and WebDialogs fits,” says Mike Gotta, an analyst with the Burton Group. “If IBM does not capitalize on WebDialogs’s relationships with resellers and partners then this might turn out to be much ado about nothing. If they don't get any other ecosystem around WebDialogs then it looks like a panic move to do something versus Microsoft and Cisco.”

Those two giants are on a collision course to compete in the real-time communications space, but on Monday the pair held a feel good session starring Microsoft CEO Steve Ballmer and Cisco CEO John Chambers to profess their intention to collaborate, integrate and fight fair so users would not be left out in the cold.

IBM has existing partnerships with Cisco around unified communications, including a March 2007 agreement to deliver integration among their real-time clients and back-end servers, as well as, an open client framework for developers.

There is a complex web of partnerships emerging in the unified communications market that includes IBM, Cisco, Nortel, Microsoft and a host of other vendors racing to provide the front-end and back-end tools needed to support real-time communication via voice, video and text.

For IBM, whose Sametime platform dominates the on-premise market for IM, presence and conferencing, Wednesday’s acquisition fills a hole in its real-time communications and collaboration lineup that has repeatedly drawn criticism.