I believe the trial period includes the streaming.
See: http://www.amazon.com/gp/help/customer/ ... =200572880
Part of that is:
Prime instant videos provide unlimited, commercial-free, instant streaming of thousands of movies and TV shows at no additional cost with a paid annual Amazon Prime membership, which also includes fast shipping along with other benefits. Prime instant videos can be watched instantly on a Mac, PC and nearly 200 models of Internet-connected TVs, Blu-ray players and set-top-boxes that are compatible with Amazon Instant Video. All of the movies and TV shows are commercial-free and some are available in HD.
To watch Prime instant videos, you must be a member of Amazon Prime. Amazon Prime is a membership program that gives you unlimited fast shipping on all eligible purchases for an annual membership fee. Amazon Prime members also get unlimited, commercial-free, instant streaming of thousands of movies and TV shows.
If you are not an Amazon Prime member, you can try an Amazon Prime membership by starting a free trial (restrictions apply) by following these steps:
After reading that it appears that the trial period includes the streaming since they say to try the streaming by starting the trial period.