Is it possible to buy a Pre and use it today? Do you need long-gone authentication servers, etc? Always wanted one, and am working on a new mobile Linux project. I think there’s something to learn from webOS.
The short answer is yes. If it's been reset, then you will need to use a tool to bypass activation. Palm back up and App catalog are gone, but manual backups can be done and there are alternative sources of apps.
You are advised to get a device running webOS 2.0 or higher. That's a Pre2, Pre3, Veer or HP TouchPad. Earlier Pre phones can be unofficially upgraded to webOS 2, but are less powerful and reports of how well it works vary. Fixes are usually more available for webOS 2, so earlier devices aren't so useful.