as for me, when im in my hometown in kampar perak, i also cant receive call when someone calls me, sms ok, i believe the maxis tower in kampar somehow not pacth/update properly in order to use with maxis 3G sime card in, when i turn off my 3G signal i can receive call etc, there was no problem when im in here in shah alam or other place,

i using sg set iphone and my brother also using aus iphone( last month ) and now using UK set also got problem only in our hometown...

anyway TS where is the place you encountered this problem? how about trying to use it at other places and see how it goes, example at your work/study places.