So this really pissed me off. When my phone battery is as low as around 50%, I can not make the phone call, SMS or any data communication, although I have checked and the power save is not on. The signal icon is on, but simply can not do the GPRS job. and sometimes, the signal icon can disappear and a network unavailable icon pops out. So if now I switch the phone off and on again, the battery is only 5% left!!! And NOW, all the data operation is back to normal. I really don't know why. Because if I try to reboot the phone at battery 80%, it will not drain up the juice. I am totally confused. Anyone has a similar issue?