I just got the free 200 MB plan.
I "purchased" a nano sim off of the tmobile website a couple months ago. The sim price was free with free shipping, so purchased isn't really the right word
I powered off my ipad 3, then I took the ATT sim out and replaced it with the tmobile sim. I then booted the ipad and turned on cellular data. The ipad auto recognized my tmobile sim. I didn't know what to do next so I opened up safari. I was immediately taken to a tmobile registration page where I was asked for my name, date of birth, zip code, email address, and a password and pin for the account. I put in all the info and submitted the form.
Poof, a couple seconds later I got a confirmation screen with my mobile number (don't know what that is about) and a confirmation that my sim is enrolled in the free 200mb plan.
I'm posting this note on tmobile cellular. In my town, unfortunately, we don't have LTE, so the status bar reads 3G. But hey, it's free!
So, you don't need a 10$ plan, if you own your device. Just put in a sim and go! cool!