I unfortunately don't have a smartphone YET, but I bookmarked this site and will definitely visit it when I do!
NOTE: Before you read, I just want to say that although I don't use this program myself, I did a bit of research and found that it is totally legitimate and highly rated. If you Google, "MobileXpression Scam", you'll see that almost all results are reviews/sites that say it is legit.
From the site:
MobileXpression is an elite market research community dedicated to improving the mobile Internet. Join today and win one of many exciting prizes in our Instant Rewards game. Everyone wins a prize! Plus, by keeping the MobileXpression software on your phone, you’ll be eligible for entries into our Weekly Winners Sweepstakes with prizes awarded each week!
More about rewards:
In addition to the incentive you receive for joining today, we provide our MobileXpression members with opportunities for cash, gift cards, and merchandise.
Just for joining, all MobileXpression members are eligible to participate in the "Your Opinion Matters" sweepstakes which offers a chance at the Grand Prize of $100,000. One winner will be chosen each month who will win $100 and will then have the chance to win $2500, $5000, or even $100,000.
Plus, as an active member of MobileXpression, members are eligible for weekly prizes in our "Weekly Winners" sweepstakes. Each week a new prize is awarded. We’ve given away iPads, Kindles, digital cameras, and many other exciting prizes.
Click here for more info!