I encountered the same.. I brought mine in the nearby authorized samsung center and the tech personnel had it reset an reinstall the software and it works. He told me to observe it for a week more or else they will bring my unit to the main sevice center and have the mother changed. But thanks, it didnt crashed, lagged, force close, etc anymore. My only problem is that my sms and fonebook still hang, but very seldom, unlike the very first time i used it for phone features. But nonetheless, im happy of the result. It wont need to change the motherboard. I am also looking forward for the 4.0 upgrade, cos it might also address the problem