This is an app for looking up unknown callers or sms-senders on your Windows Mobile device, it requires .net compact framework 3.5 A forum thread at XDA Developers contains all the discussion regarding the development and relases for other languages.
The software is open source and hosted by sourceforge, just hook into the SVN and download the code...

• Free
• Auto-lookup unknown callers
• Manually lookup unknown sms-senders
• Manually lookup unknown outgoing calls
• Checks if the call is from a telemarketing company
• AppToDate integration

Download the norwegian version here:
CallerUtility.CAB