Hello!
I have my older iPhone 4 and it's already been updated to the iOS 7.1.2! Apple's iOS 7 comes with Personal Hotspot issues ( Some iPhone users are can't activated their Personal Hotspot function on iOS 7 and iOS 8 )
Since my iPhone 4 has been updated to the latest iOS 7.1.2 ! Personal Hotspot function doesn't work ! I have tried and this ways works for me. Now my iPhone 4's Personal Hotspot works without any problems !
Let's see!
Turn on your iPhone then follow these steps! Your iPhone must connected to the internet!
Open up Setting/Cellular/Cellular Data Network
Cellular Data Network contents:
Cellular Data
MMS
Personal Hotspot
Our target is Personal Hotspot! Of course, Personal Hotspot requires
APN
Username
Password
Now you are must create an account ! I mean Personal Hotspot Account! Don't worry ! It is very simple and easy too. Enter your optional Username and set up optional Password ! And APN field is must be leave empty ! See below:
APN: ( Leave empty )
Username: iPhone ( Optional )
Password: 1234567890 ( Optional )
Now go to the back " Setting " and wait until appears Personal Hotspot icon on your " Setting " ! Enjoy your Personal Hotspot ! Try it now
It is works with my iPhone 4 iOS 7.1.2, iPhone 5 iOS 8.1.2 and iPhone 5S iOS 8.1.2
Unfortunately! You can't downgrade any iOS devices
Good Luck!