No. Not me. Another person who was having problems getting the SIM to stop pestering him signed up for the Free T-Mobile plan. I don't personally know a thing about it.
I'm on Verizon, and I'm most certainly paying for it.
If I remember correctly, it was one of the options he had as a new iPad Air 2 customer with the Apple SIM installed. This SIM lets you sign up with a couple different providers from the iPad's cellular settings; similar to how you could sign up to different AT&T plans with the first iPad.
Here is the thread again:
http://www.ipadforums.net/threads/cellar-data-reminder.124771/
It was post # 15. You can try asking the OP (Original Poster) of the thread, but it doesn't look like he's been back to visit lately.
Anyway, I didn't mean to sound like I knew about the T-Mobile plan personally, or any of the details. It was just an idea. Something for you to look into. If you can't find it in T-Mobile's offering at there website, then it's probably not an option.