If you "activate" but not "unlock" you can use the follwing:
- iPod
- Wi-Fi
- Mail, Safari
- Calendar, Address Book
- Google Satellite, Goodle Maps
- Camera
- Calculator
- Extra apps via AppTapp
.. in short everything except Phone (and thus phone-related like voicemail etc.), YouTube, and extra apps that use EDGE (so no networking without Wi-Fi).