Why didn't Microsoft have a backup? That's the big question following the incident that has left many T-Mobile Sidekick users unable to access contacts, pictures and other personal data via their phones.

It turns out the company did, in fact, have a backup database, a Microsoft representative said in response to our inquiry this morning. However, it looks like the setup wasn't good enough in this case, because the company says the backup was also "impacted" by the initial server failure.

Microsoft is involved because of its acquisition last year of Danger, the company behind the Sidekick software and services. Over the weekend, T-Mobile said the "likelihood of a successful outcome is extremely low," but Microsoft offered a glimmer of hope this morning -- saying that it's still "investigating solutions that may enable data restoration." Here are Microsoft's answers to questions we posed via email.

What caused the problem? "A server failure at Microsoft/Danger caused an outage that affected the applications and services available on the Sidekick devices. Microsoft / Danger has been working non-stop in close coordination with T-Mobile, and engineers from 3rd party technology suppliers to restore the most critical services first, testing each phase along the way to ensure full functionality."

Why wasn't there a backup for the data? "There was back up for the data. However, the initial server failure impacted both the main and backup databases, so the data recovery process has been incredibly complex. We are currently investigating solutions that may enable data restoration. We will post an update on this issue as soon as we have more information."

Will this prompt Microsoft to review its policy for data backups? "This was an extraordinary situation where we suffered a confluence of errors that obviously caused substantial problems. We greatly apologize for these and have been working around the clock to restore full services. We have a full team working in parallel with the restoration team to augment the redundancy and stability of this acquired service over the long-term."

Had Danger been transitioned to Microsoft servers, or was it still using its own servers? "The Sidekick runs on Danger’s proprietary service that Microsoft inherited when it acquired Danger in 2008. The Danger service is built on a mix of Danger created technologies and 3rd party technologies. Microsoft’s other cloud computing projects are totally separate from the Danger Service and do not rely on the Danger Service technology."

Update: Ina Fried of CNet News.com notes that T-Mobile has halted online sales of the Sidekick, at least temporarily.