Just upgraded official firmware available at http://europe.nokia.com, restored the data from memory card and finally installed bluetooth keyboard plugin and GPE PIM suite. Nokia keyboard works well with Notes, Web, and E-mail applications. In contrast to former upgrades, all data including contacts and calendar from GPE PIM suite were successfully restored (!!!).
To find right settings for VOIP application is tricky, but even a call to landline using gtalk2voip.com finally worked great.

I would like to thank ITT forum members for useful tips and references, making it easier for users to get 2006OS applications work!