I just went through this with Boost. You may need to contact T-Mobile to find out if they provide a service to block. Otherwise you also may be able to make a profile and add all of your contacts to it. Name it something like "Rec. Contacts Only". It worked on my old service, but I'm fairly new to T-Mobile so don't know if it will work here. My old phone had a profile built in for that. I'm using an LG GS170. Not a fancy phone, but does the job.