The 'Personal hotspot' option is gone from my iPhone 4. Why? The 'Personal hotspot' option is gone from my iPhone 4. Why? Is there any way to get it back?
Make sure you have an APN + Username &amp; password set under Settings > General > Network > Cellular Data Network. The bottom option "Internet Tethering" has to be filled in to enable Personal Hotspot.

Apple KB article - iOS: About cellular data network settings (viewing or editing the APN)