Xseries :: Nokia X6 Shutting Down When Take/receive Call?

the phone occasionally turns off when i call, or recieve a call (i hear a click and phone turns off). i have to manually start it again. sometimes the problem persists for a few next calls, while sometimes it doesn't. anyways,i usually let it be for a day or two, and use my old phone. but this is getting really frustrating now, after all, i bought it to use it!i have tried the hard reset, the factory reset. i took it to the official repair shop here in my country, where i demanded they take away the **bleep** vodafone, preventing me to update further than v20 firmware.the repair shop gave it back, saying there are no more problems. im taking a guess even they did those soft/hard resets. i have the latest firmware (v30) and yes the phone does work much faster, but just now i did get another shutdown when having a conversation ! i even uninstalled pretty much all not needed apps (facebook, Internet, accuweather, games, ...) on the new firmware.i cannot have such a unpredictable phone, especially when i am working and have to take important calls. imagine how it is, when the phone dies in the middle of important conversation with the boss/costumer.