Joe from iTweakiOS explains the hack:
“So you want free hotspot on your iPhone or iPad but don’t have a jailbroken device, huh? Well, I come with good news for a lot of you today. Many of you may remember a story I put out awhile back talking about how CommCenter blocks edited carrier.plist files and I may have found a work aroun to get things like personal hotspot enabled. Well, I’ve found the solution, but first, let’s talk about why CommCenter blocks plist editing. This happens because of the very thing we’re doing right now, which i suspect will likely be patched quickly by iOS 7 GM release time.
People were enabling tethering by modifying the original carrier.plist files and this stopped entirely when Apple implemented signatures into the carrier.plist files and creating what we all know as CommCenter which is the process that checks these signatures. So, the challenge was finding a way to enable hotspot without CommCenter checks and verifications. After months of research and digging, I’ve finally found a genuine workaround to enable this great feature and its quite simple, really.”
As usual, the workaround explained above comes with a significant asterisk. Things can get a bit sticky when you start editing .plist files, so we recommend that you backup your device before attempting this. Also note that the exploit used for the mod will likely be fixed soon.
If you want to give it a try, you may like to follow this step-by-step guide posted here. The author of the tutorial claims that the method has only been confirmed to work on T-Mobile, and he recommends that you have an unlimited data plan, as gigabytes can add up rather quickly.