My iPhone 3GS has been randomly restarting itself

The screen goes blank then the Apple logo appears, after a few seconds it returns to the home screen and whatever I'm doing is lost. It has been doing this every couple of minutes all day yesterday, then this morning it suddenly returned to normal. What caused this and how can I diagnose/repair future issues?

Added (1). The phone is switched off all night and it started when I switched it on yesterday morning.

This happens with old phones. You should turn off and on your phone atleast once a day to keep it from happening. If it still dosent work take it in to apple

Because this is iphone
it can do anything

It'd gone into a restard loop. Same thing happened with my ipad and i had to restore it with iTunes. Everything is fine now except the fact apple maps suck donkey's balls.

You can try turning it off and once it is off, turn it back on.
You can do that by holding down the off / on button on the top of the phone, then sliding the
slider to the right when prompted.

It is unlikely that will work as your phone has been turning off.

So restoring the phone through iTunes would likely be the best option.
If you have a Mac computer this is simple, you plug your phone in via its USB cable, and select the phone in the left hand panel of iTunes, and select Restore, don't unplug the phone from the computer until it has been completely restored.

Here are the instructions to restore your iPhone using iTunes:

http://www.ehow.com/...tunes.html

Hope you have backed up your phone.

Otherwise you may have to user a friend's computer to restore your phone, or contact Apple.

Get into an Apple store and make it check with them. They are very helpful and if within 1 year, its free as well.

A hard reboot might be a good solution, which is very simple to do.