Mobile phones are not only for communication anymore. Nowadays you have all sorts of apps for all sorts of things. But before those hit the markets they have to work well. And how can you guaranty quality? By testing the apps. The tester has to spend some time and effort to discover bugs and things that are not working quite well. You will be paid for this job.
uTest.com is a company that hires part-time testers for this purpose. And if it turns out that you are good at it you could probably do this full-time.