If you're the Primary Account Holder, you can add or remove Message Blocking on My T-Mobile or through the T-Mobile App. Learn how to change this service on your account.
If you're having trouble finding Message Blocking when following the steps for changing your services, please contact T-Mobile Customer Service.
Things you should know:
You can block incoming and outgoing text messages (SMS), picture messages (MMS), Instant Messages (IM), and email.
Messaging Blocking is intended to block all messages, not to prevent overages.
Message Blocking will block text and picture messages even if you have a messaging feature on your account.
Message Blocking won't block instant messages or email on Windows Mobile or BlackBerry phones.
Found this on the T-Mobile site hope it helps