Many ideas on phones and apps as well as complaints about them are found in social forums that target mobile users and developers. The complaints and comments from users are great in terms of feedback as it will tell you what not to do with your app, what not to buy, what brand is good and so on. Users and developers will also tell you what you should avoid when creating your app due to design complexity and programming tool restrictions. Most of these targeted social forums are free and you only need to register to participate in them.
Another avenue to get ideas is through focus group gatherings. These groups should be represented by age, gender, profession and other denominations. The analysis and results from these focus group gatherings will clearly show where your intended target group market lies. It will also show what type of app is popular, which brand of phone is the best with current models, how big is your intended market and what price level is acceptable. These focus groups will also tell you what is good about the app, what is lacking in the app and what is not good about the app. You will now have insight into what is good, what is missing and what to avoid when designing an app for the mobile market.