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In our company we use Ubertesters service - they provide all-in-one platform for mobile app testing, and we can also hire their testers in one click (only when we need them), it's very useful thing.
Anyhow, you can use their platform (I assume they have some free plans as well - http://ubertesters.com/plans/ ) even if you don't need testers - it will help you to manage the testing process, i.e. to distribute builds over-the-air, send bug reports from you mobile device (with a screenshot editing feature), generate reports, track sessions of other testers and so on. Recommended.
Selenium 2 offers both iphone and android testing. They are experimental.
Try the above links, hope it will be benefical for you. Mobile app field has seen a tremendously growth today. It is good to see that the users are using it in a right way.