Summarise from danaty.org

The first thing you must do is to decide what you exactly want. There are all kinds in the market today. And they all serve different purpose different needs and people. Even the blind now have their kinda phone. Hope you are aware.
•How much are you willing to spend?
•Determine the phone carrier you want. Some of them are: Verizon,AT&T,T-Mobile,Sprint etc

•Call quality: clearity,volume etc
•Design: are you comfortable with the size colour,shape,screen touch etc
•Operating System: the operating system determines how the phone works. Some OP are: Googles Android,iOS,BB OS,Microsofts Windows.
•Display: screen size and shape. If you want to browse with your phone then go for a large screen phone.
•Screen Resolution: If you intend to read on your phone a high screen resolution will do
•4G support availability. Consider data and download speed
•Camera: If you are photogenic
•Processor
•Battery Life

SUMMARISED FROM SOURCE: http://www.danaty.org/how-to-buy-a-mobile-phone/