Personal Hotspot just appeared by itself (Sprint iPhone 4S)

This morning Personal Hotspot appeared in my Preferences app. Earlier it was definitely not there; when I launched it a bit after 11am it was right there in front of me. I changed nothing on my phone, and I know I don't have the Personal Hotspot add-on to my plan...So why did this appear now, and what would happen if I turned it on?

I received my phone on 11/11, the day that Sprint supposedly started locking SIMs. I don't know why the hotspot option shows up now (didn't jailbreak my phone, didn't update any software...) or what it would do (and if I turned it on would I automatically get $30 added to my plan)?