iPhone 4 buzzing on Temperature Warning!

Recently bought an iPhone 4 from Singapore for a premium price. Bought it outright, got it jailbroken and stuff. Worked fine, downloads awesome but I felt guilty and signed up for iTunes. Gonna see my credit card bill fly high soon. 2nd of January 2011, my Whatsapp was beeping so I picked up my phone and had a look at it, it was flashing with a 'Temperature Warning' and I could do nothing other than make emergency phone calls. It had to temporarily halt everything as the phone was over-heating. My phone was left on the table and was untouched for the past 3 hours or so. I rebooted the phone and it worked as normal again till today. But its been only 3 days since. If this warning still persists I shall be heading to the phone shop. Grrr! So not funny.

Force restart the iphone and you it will return back to normal again. This happened 3 times in a year. It is still bearable. All 3 times were while multiple whatsapp messages were flooding in at the same time.