I have a SIM for data on my iPhone when I’m in Indonesia on the Telkomsel network. Unfortunately the option for “Personal Hotspot” was no longer accessible. I found these instructions for an older iOS version, and was able to easily modify them for iOS 11.
- Go to Settings > Mobile > Mobile Data Options > Mobile Data Network.
- On Mobile Data and Personal Hotspot section, enter internet in the APN field.
- You will now see Personal Hotspot is available in the main Settings page.
Full credit to mamaz for these instructions. I just had to translate Cellular into Mobile because of my localisation settings.