I have exactly what KYLEB has, and it works great.
It has a whitelist for approved phone numbers, all others are ignored.
The only hassle I found was getting your T-Mobile online account access set up. Their security requires sending a text with a code to the phone number. Even their help support can't get around that. I put the SIM in an old phone we have, to get it set up, and made my iPad a 'trusted' device so now I can access my account to check on and add $$ to the account when desired.