I talked to Maxis (telco), they said it was iOS problem, without knowing that I hv upgraded to IOS 6.1.3, they told me after upgrading to 6.1.3, problem should go.... To cut the long story short, I ended up calling Apple which agreed I it is hardware problem and they gv me the so called Penang Apple Centre but I was then asked to talk to Maxis :-s
Whatever it is, the conclusion is the whole Apple team (Apple & its partners) *****. Such thing will not happen in Western country as Apple does not respect Asian, does not respect our consumer's right. My friend had a Mac Air which the local apple centre refused to fix, got it fixed in UK.
Just like you, I don't have another phone to use. Maybe we should report to Tribunal of Comsumers and get a refund, then we should but other smartphones.
Since iPhone 3GS, I converted my whole family to iPhone 4, I got myself a Mac Air, Apple TV, iPod, iPad 1, iPad 2, iPad 3, iPad Mini, iPad 4 and this BAD iPhone 5, I will put a full stop here. I think Apple needs Steve Jobs to come back....