In one other aspect if you see that you have more Android users as your customers who recently loved buying Samsung Galaxy , you should focus on the Android development that can produce apps to be run on Samsung Galaxy. To develop for both platforms sounds smart but you have to focus on the one which has more potential for you.
BlackBerry app development, Symbian app development and Windows mobile application development can also be smart for you, depending upon your scenario. One other aspect of Smart can be mobile app development that you have expertise in. But your expertise must match the requirement of current time. And you always need to be up to date with the latest tech news around the globe and tech news portals like Gossipfunda are giving you just that.
As currently iPhone and Android are hot topics, you must groom expertise in these areas. You can also target future and make long term plans such as analyzing the current trends that shape future. For example, after the Nokia and Microsoft strategic alliance for next generation mobiles, soon a time will come when Windows mobile app development will become a hot topic. So what you can do is try to focus on this one side and build your expertise in it that will help win tomorrow’s competition.