Ok, update on mine;
It's working 100% for one and a half month now. What I did? Nothing! I got pissed back then and just put the phone away (with battery detached) ina drawer and forgot about it. After a long time, I got it back bc I was going to send it over to a friend in Finland to get it fixed but before I needed to be sure that the problem was still there. Result: worked 100% since then.

My veredict? Humidity! My phone also had a issue with the keyboard slider sensor (that kept triggering off alone) and that one started when I travelled to oh'beautiful'rainy London. And of course I walked a lot in the rain. Also, the day it stopped recognizing the sim was at my graduation party (which also rained quite a bit).

As far as my electronics experience goes this humidity-related problems are "known" to go away after long periods of time, resting, in dry environment.. that's what I did and it worked. It seems a good theory for me..