I am currently trying to get a refund from MLB.tv. Don't believe the ads that say, "Watch all the games on your favorite device". I have all the requirements needed to watch games. I have an HTC phone with Android 2.2. They are now saying this phone will not be supported. Also the tablet I have was just able to get games.
If you want to go to MLB.tv, go to their support forums and make sure your "Favorite Device" can actually do everything they promise.
I have a Roku and have had a bad problem with rebuffering. The Panasonic Smart tv I have doesn't have any of the extras they promised, such as watching 2 or 4 games at once. They didn't tell me thayt until AFTER the date I could get a refund. My internet download speed is a consistent 8 Mps. The minimum they require is only 3 Mps, but it still rebuffers at least once an inning.
Some people have had a lot of luck, hope you do too!
Forgive me but it sounds like you have some non-traditional devices. I have a PS3, dell laptop and an iPhone 4 that all work fine with it with no problems on 10MB internet. What kind of phone do you have? Is your Roku an older one or one that supports HD?