Yes, I had that problem too and you guys scared me to death, that the comm chip might be dead. I opened up the back cover, got the SIM out, and with the tip of my screwdriver i scratched out some lines exactly where the pins on the SIM reader should be. Scratched out a little (be gentle, very gentle, treat it like you would treat your girl) the pins on the SIM reader and voila, it works perfect.

After this fix, I even applied some pressure in key points, even shaked the phone like crazy, no more signal loss. Everything is ok. Also, my SIM is a little more slim than other sims, idk why, but it just is so on a shock like a fall on the bed it would loose signal for ~1 second, but I got rid of that error.

Here is a pic with the scratches on the SIM: