The lawsuits came after a number of T-Mobile's Sidekick PDAphone users were informed earlier in the week that their online data - held on services operated by Microsoft's appropriately-named Danger subsidiary - had disappeared into the cloud.

The Danger operation, Infosecurity understands, designed and developed the software for T-Mobile. The cloud data loss saga is seen by many industry experts as the largest failing for cloud computing in recent times.

Following several days of negative media reports, Microsoft said it is now able to recover the lost coud data and has staff working "around the clock" to reconfirm affected users contacts information, before moving on to recover other elements of the lost data.

Industry observers were expecting a possible lawsuit between T-Mobile and Microsoft's Danger subsidiary, but the class action lawsuits appear to have caught everyone by surprise.

In the first lawsuit, a T-Mobile customer has asserted that one of the major selling points of the Sidekick service was that users always had access to their personal data, and that the data would be entrusted to T-Mobile to maintain - and retain - safely and securely.

The second lawsuit claims that T-Mobile's advertizing did not disclose that the firm had no backup to ensure that customers' stored data could be retrieved if there was a failure.

For its part, T-Mobile said it is confident that it will now get most of the data back, and is offering US$100 vouchers to those whose information has been "lost".

As news of the lost cloud data surfaced earlier this week, T-Mobile halted sales of the Sidekick PDAphone.

The BBC quoted Harry McCracken, the editor of Technologizer.com, as saying the incident "is the most spectacular loss of data on the web to date."

"There have been other examples, but always from small companies. For this to involve a big name like Microsoft is a major embarrassment and a big worry for consumers and Microsoft."