For me this problem was not related to the SIM-card.
I tested a number of different cards from different service providers, all real MicroSIMs.

I also had this issue with all the N9 phones I have owned (I think I am on my sixth N9 right now. Tend to get irritated on them and buy something else but then I miss them and go back). Thus quite sure it is not HW failures in some single devices but a design flaw present in all the phones.

On the other hand, I have numerous friends and colleagues not having any trouble at all with their N9 phones which indicates that the problem is caused by a combination of things.

//j