Microsoft has agreed to buy software firm Danger Inc, maker of T-Mobile's SideKick web phone.
Hilton is among stars who have given Danger a cool cachet
The gadget, also known as the Hiptop, has been popularised by a number of American celebrities, including socialite Paris Hilton.
Danger was co-founded in 1999 by Andy Rubin, Joe Britt and Matt Hershenson. Mr Rubin has moved on to a new job running Google's mobile venture.
Microsoft did not disclose the purchase price as it made the announcement.
A statement by Microsoft highlighted the fact that it saw Danger's customer base as "young and enthusiastic, internet-savvy and socially inclined".
The statement added: "The Danger team has a deep understanding of consumers and a hold on what people want from mobility, making it an ideal group to work with in delivering connected experiences."
Speaking at the Mobile World Congress in Barcelona, Robbie Bach, Microsoft's president of entertainment and devices, said: "It completes the picture for us in terms of making the transition from just being on the business side of things to being on the consumer side of things."
The SideKick allows users to instant message, talk on the phone, send e-mails and access the web, with a distinctive swivel screen that flips around 180 degrees to reveal a full keyboard.
Mr Rubin has said in interviews the company was called Danger because he had bought the danger.com domain name several years earlier. The name was a reference to a robot in the TV show Lost in Space, which continuously issued "Danger!" warnings to the cast.
Michael Gartenberg, analyst for Jupiter Research, said on his blog that news of Microsoft's acquisition was the "real excitement" of the first day of the Mobile World Congress.
He added: "The T-Mobile SideKick has had moderate success in the US markets appealing to celebrities, sports figures and of course all the demographics that look up to these folks.
"The SideKick had strong appeal as the anti-Blackberry for younger audiences and it will be really interesting to see how Microsoft integrates the technology, business model, and overall device cachet to a culture more at home to selling to enterprise CIOs than it is to selling rock stars."