@coderus: Yep, I can browse through my address book when I select 'Add contacts'. Somehow most contacts are displayed multiple times, first only as numbers, then with the name and then some even for a third time in a consequent list. When I select 'Sync all phonebook', it just goes back to my conversation list and nothing happens. Same if I try to add contacts one by one. It seems like a contact is added to the list if I receive a message from them. Like my work phone number from which I received a message, is now in the list along with the groups.

@tiempjuuh: I'm not quite sure how to do that but I'll see if I can figure it out However that's only related to not being able to add contacts, right? Or could it have something to do with not being able to send (and receive) messages too? Thanks!