I'm having the same problem as described by slaapliedje and Grazy.
All of a sudden my N9 started to loose the signal. And no matter what I do, it keeps telling me, that there is no signal or no sim card or a problem with the sim card.
I reboot, I take the sim out and back in again, I enter my pin code a thousand times, and then maybe it comes back to life. Or I just do nothing and after an hour it is back on its own.
it's very strange and very annoying. now I ordered a new sim card. hope this will fix it.
but when I'm reading the comments here, my hopes are low. because actually I think this started after I installed PR1.3. never had the problem before that.....
I will report back, if the new sim card will do the trick.
Anyone with another advice / experiences?