Hi, I'm having the same problem. Wi-Fi is working fine but I'm unable to switch on the Mobile Data app. All my friends are using the same carrier but their handsets are showing the 3G signal not mine. Since last two days this problem is there. Also, I had received an update from my both the service providers, it was about some MMS thing, which I duly updated. Can this problem be because of that ??? Pls advice & help.