Not sure if anyone noticed previously, but the T-Mobile Visual Voicemail also worked in a trial version for 30 days, but you didn't have to cancel. It would be in trial until the trial was over and then just act as a voicemail application (without the text conversion). Based on how that application operated, I'm pretty certain that the Scam Shield also operates in a 30 day premium and then changes to the standard free version once the trial expires, that the customer need not do anything further. In fact, I had that experience, it's just the free version now and doesn't say anything about being Premium any more.
I noticed that I have 57 blocked calls since I received the application. Seems to have blocked much better than the prior Name ID application.
All in all, I'm pretty happy with the free version. I do get the "Get the full experience upgrade" bar above the menu when I'm in the activity menu, but that's not a problem. I just don't click it and do what I need in the app.