Over the weekend, the two companies told users that all the personal information stored on their QWERTY keyboard-equipped phones, including phone numbers, addresses and appointments, was gone – most likely for good.
Now, all visitors to the Sidekick's Web site are greeted with an apology. The phones are made by Microsoft's subsidiary Danger and sold by T-Mobile and, in the Web site's message the two companies say all information has "almost certainly been lost as a result of a server failure."
Tech analysts and top bloggers say the data loss is damaging to the companies' reputations and a warning about the risks related to saving data only in the so-called "cloud" and not on owners' hard drives or personal computers.
Although a Microsoft spokeswoman told The Associated Press that there was still a chance that some lost data could be restored from a backup system, T-Mobile says regardless of that outcome, they will automatically credit one month of data service to those who subscribe to T-Mobile Sidekick data plans.
The benefit of a cloud storage system is that if a user lost a phone, saved data could easily be downloaded to a new device. But unlike newer phones, the Sidekick didn't give users a way to backup contents locally, on a computer or elsewhere.
"It's the perfect storm of chuckle-headedness," said Dan Tynan, a technology reporter and co-author of the technology humor site eSarcasm.
Given the Sidekick's data storage system, he wondered how Microsoft didn't ensure real-time replication of the data and provide up-to-the-minute backups -- or, if it did, what went wrong.
It's not known how many customers have been affected by the loss, but The AP reports that, judging by T-Mobile's financial statements, the figure could approach 1 million.
Tynan said that it's rare for a major company to suffer such a severe screw-up but helped ABCNews.com come up with a few other recent technology disasters. Here are six more.
In what has been called the largest credit card crime of all time, earlier this year, Heartland Payment Systems announced that hackers had broken into the computers it uses to process about 100 million transactions each month for 175,000 merchants.
The hack was uncovered in January, after Visa and MasterCard notified Heartland about suspicious transactions. Heartland processes card payments for restaurants and other businesses.
In August, three men were indicted by a grand jury on charges related to masterminding a scheme to steal more than 130 million credit and debit card numbers and personally identifying information from Heartland, 7-Eleven Inc. and other companies.
According to Information Week, Heartland said in August that the breach cost the company $32 million in legal fees, fines, settlements and forensics, so far.
In November 2007, the British government acknowledged that it had lost two disks containing personal information for 25 million Britons. The two disks were dropped into internal government mail but never reached their destination. The disks contained detailed information, including bank account numbers, names and addresses.