Today I had my first bad experience with Apple products after 5 years of using Mac, iPod, and iPhone.
This morning I got my brand new iPhone 4S 16GB from the US. After unboxing the phone I switched it on and the Apple logo appeared on the screen. Here comes the sad part of the story; the screen showed the Apple logo (as usual when all iOS devices boot) and then the logo disappears as if the phone is starting the welcome screen but suddenly the screen turns off for a second then the Apple logo appears again (as someone has restarted the phone).
One point I want to mention in addition to the above is that every time I leave the device for several minutes doing the same scenario (Apple logo, screen turns off, Apple logo again) over and over again suddenly I get the welcome screen where you have to slide the button to start configuring the phone. However, when I do so, the phone screen freezes for 2 seconds and then the phone went back to the same old scenario.
I tried all the possible scenarios (force restart, restore through iTunes, change SIM card etc...). From my experience with electronics and iPhone (I'm an iPhone user since 2 years and owned the 3GS and 4) I think it's a hardware issue. If so, I have to ship it back to the US as I don't live there and I got the phone from there.