If you are not a mobile app developer, then this how you can use mobile apps to make money:

Apps that help you work for money
Field Agent - As “agents” you use your phone to provide photos, scan barcodes, verify locations, complete surveys, mystery shop, and perform other useful services for the website's clients.
Gigwalk -  Choose from “gigs” of all kinds, from photographing business locations for search engines to testing new mobile apps - basic pay is 4 dollars.

Apps that pay you for your opinion
iPinion  - Get reward points for answering surveys and redeem them for cash or gift cards.

Apps that pay you to check out apps and sites of sellers
Checkpoints - Earn gift cards, free merchandise, game points or credits and airline miles for “checking in” at storess.
Shopkick - Earn "kicks” for checking in at shopping locations, scanning items and for making purchases. You can redeem these earned "kicks" for merchandise, gift cards or discounts.
WeReward  - Earn reward points for check-ins and tasks, such as taking a photo of yourself with a product at a participating business.

Sell stuff on mobile phones
eBay Mobile
GoPayment

If you liked this, please check out The Success Manual -  200+ top things we all should know to succeed faster in any career.