How can I enable Personal Hotspot on iOS 7 even though my carrier has disabled it?
If you're willing to jailbreak, you can use TetherMe. It will enable Personal Hotspot then change the location of the data to appear to be coming from inside the device, thereby bypassing the carrier's disable.

 TetherMe
Dynamically enables native tethering or personal hotspot for iOS3.X or newer devices. This should work on any carrier without the need for customised bundles or preferences.
TetherMe has been tested to work on all iOS versions from 3.0 to 6.1 and works by telling the iPhone to allow tethering on any APN that is used for iPhone data. As a result, you should not be charged any more for tethering data than normal data by your phone company as all tethering data appears to come from the phone itself.