If you are watching ads and answering questions via your mobile it's one of two things, you are either participating in surveys for free minutes or alternative you are paying to watch the ads.
Someone I know tested it out and said it took a while to get a few minutes, so not good unless really scrapping for pennies. Then you have to wonder how you have internet access.
I don't know much about the US market but in UK virgin has tied up with orange and they give the best deals in the market. There are lots of conditions added to these kind of offers so be careful.
I should try it out! I have been with them for about 4 years. They really should consider giving long time customers some free minutes, lord knows how much I've spent!