Microsoft admitted over the weekend that a technical problem has resulted in the loss of contacts, photos, and other data for unlucky T-Mobile Sidekick users. For more than a week, many Sidekick users have had trouble accessing the Internet, phone contacts, and calendar appointments that are stored on servers operated by Microsoft. Now, online access is restored, but many subscribers might not ever be able to recover their personal data. People who reset their Sidekicks by removing the battery or allowing all the power to drain away are most at risk of losing the phone's information. There are more than a million Sidekick users. The snafu is an embarrassment for Microsoft, which has been trying to turn around its reputation in the cellphone industry.