Broken tethering ios7. / no Downgrade?

After upgrading to iOS 7, on both my iPad 2 and my iPhone 4, my bluetooth tethering would no longer pair nor connect.

Apple store could duplicate the problem, but without warranty, wouldn't give me the iOS6 based phone to replace the "upgraded" iOS7 iPhone 4, and couldn't downgrade the iPhone 4 to iOS6 so I'm stuck buying a new phone if I want my tethering back.

Any way to get back to iOS 6? I understand the upgrade is irreversible?

Bill