Currently, T-Mobile offers the following services. I've pulled screenshots to show you:
You can definitely add these services on myT-Mobile. Log in, then choose the plans tab. From there, select the specific line and click the magenta-colored button Manage Data & Add-Ons. If these services are unavailable to you, you should call a T-Mobile rep., 611 from your T-Mobile phone.
Manage your T-Mobile account