Rotation Lock iOS 4.2.1 iPhone 3GS

[Markleshark]

I apologise in advance if I'm being stupid.

My iPhone 3GS with iOS 4.2.1 seems to have rotation locked it's self. I didn't think this was a feature on the iPhone, but I have what I believe to be the symbol on the home screen, and the device certainly is rotation locked. I've not asked it to, was closing some open apps earlier and now the symbol is there and it's locked.

Am I missing something? Short of restoring any way of fixing this? I've tried simply restarting the iPhone but still locked. The mute switch does nothing either (well, aside from mute the phone, of course).

Thanks,
Mark.

 

[Markleshark]

Tried to edit, but the advert covers the button in IE.

Just wanted to add, no hacks or jailbreaks. Screenshot attached.

 

[hockeyhammer]

double tap the home button as you would to multitsak, then swipe to the left, there will be play/pause, next track, previous track, an ipod icon and a grey lock icon, tap the lock icon, this toggles rotation lock