I've had a Sidekick since 2004 when I was at Technorati - it's great keyboard and integrated support for web, email, instant messaging and the built-in app store that meant I could add an SSH terminal was perfect for being on call to fix servers while commuting by train.
Another great innovation was storing all contacts, calendars, emails etc in the cloud, so upgrading phones—even to new models—meant that you just turned it on and it quickly synced up.
When I switched to Android last year, I kept the Sidekick contract (and my wife's) because the info was there. It didn't have an export option, and I put a 'write a GreaseMonkey export for t-mobile's website' on my to-do list, but never quite got to it.
Now, they say we've lost all of this data. The moral of the story is not to trust data Roach Motels that only import and don't export. Demand that your contacts store supports the Portable Contacts API, or at minimum vCard export. Check it today, before you lose yours.
"Regrettably, based on Microsoft/Danger's latest recovery assessment of their systems, we must now inform you that personal information stored on your device - such as contacts, calendar entries, to-do lists or photos - that is no longer on your Sidekick almost certainly has been lost as a result of a server failure at Microsoft/Danger. That said, our teams continue to work around-the-clock in hopes of discovering some way to recover this information. However, the likelihood of a successful outcome is extremely low"
- Sidekick™ - T-Mobile Forums (view on Google Sidewiki)