Microsoft, whose Danger subsidiary powers the Sidekick service, said it is "working urgently" to deal with the problems, which interrupted data service for most Sidekick users starting at 1:30 a.m. PT on Friday. The level of disruption has varied, though most users have been affected, Microsoft said.
"We are working around-the-clock to get all our services back online and will continue to post status updates to our valued customers as issues are resolved," Microsoft said. "We thank our customers for their patience and sincerely apologize for any inconvenience this disruption has caused."
Microsoft said that, as of 6 a.m. PT Tuesday, it had restored service "for critical applications including address book and calendar, social media applications, IM, web browsing, media player and camera."
"Our goal is to have all services restored to 100 percent functionality by Thursday; however there may be some exceptions," Microsoft said.
Read more of "Major outage hits T-Mobile Sidekick users" on CNET News.
