Scam Shield™ Premium is an application that gives your more control over your calls and voicemail. You can automatically block likely scam calls, automatically send telemarking calls to voicemail, and favorite certain contacts to make sure their calls come through.
Please note that regular Scam Shield™ (not Premium) is included for free with T-Mobile Essentials and T-Mobile Magenta. Scam Shield™ Premium is included for free with T-Mobile Magenta Plus.
It is unclear what the difference is between Scam Shield™ and Scam Shield™ Premium. It's likely that you do NOT need this premium add-on.