If you have a JB iPhone and recently switched to tmobile or were using tmobile and updated your carrier settings so you can take advantage of LTE, 4g and visual voicemail you loose the ability to do personal hotspot. I had JB iPhone 5 with tether me installed. Once I updated my carrier settings the option to tether was gone. I could only use it if I contacted tmobile customer service. Long story short if you use the program ifile you can can remove this file and it will give you the personal hotspot option back. So awesome! Download iFile or iExplorer and navigate to /private/var/Managed Preference/mobile and delete the com.apple.managedCarrier.plist file.