Game development is a tough market in general, on mobile phones especially.
In order to earn money with JME games, from my point of view, it is necessary to get paid for the game development at least partially by a company which wants to use the game in a marketing campaign.
After a brief period of time your game will be "cracked" and available for free. Therefore, money is earned only in a brief period of time directly after the launch.
In my opinion, if you want to go for money, choose another road.
