Worst acquisition ever? Microsoft has given up on getting anything out of its $500 acquisition of Danger: it's shutting down the Danger service for T-Mobile Sidekick customers on May 31.

Microsoft bought Danger in early 2008 to inject some life into its mobile phone strategy in the face of Apple's iPhone. But the acquisition was botched by internal politics and delays. The Danger team was put to work designing the ill-fated Kin phones and service, while a separate group built the Windows Phone 7 platform that Microsoft eventually bet its mobile future on.

According to internal sources, the original specs for Kin were quite advanced -- the phone was supposed to incorporate social networking and gaming, as well as advanced email functionality -- but repeated delays forced the company to scale back its ambitions, and it launched in May with no games, no instant messaging, and other serious limitations. Microsoft killed it less than two months later.

All the while Microsoft continued to operate the Danger service, which gives T-Mobile customers online storage and backup for contacts and other information, but suffered an embarrassing outage in October 2009. Now, it's shutting down the service for good on May 31. T-Mobile will give customers several options for transferring data stored in the service.

Microsoft says it used some of the concepts of the Danger service in Windows Phone and how it backs up data online. But the actual technology never made its way into Microsoft's smartphone platform.

T-Mobile is planning to release a new Android-based line of Sidekick phones later this year.