Hardware or software problem non-responsive non-stuck power button iPhone 4

Power button suddenly stopped responding.

It is not stuck as it clicks.

Arbitrarly, the phone would go on sleep while using as if someone pressed the power button! and right after the phone give me "Slide to shut down" as if someone pressed the power button for 3 seconds.

This happen when i'm on a call, and more when it is just there on my desk without me touching it.

As i didn't touch the phone and it does that, i guessed it is a software problem.

I preformed an OS update and the problem still there.

I'm in Dubai, and the weather is very hot and very humid, so i thought it is a hardware problem, but again, how would it do what it does suddenly without me even touching the unit!!!

We don't have Apple store here, just some retailers.

Anyone with similar experience?