It depends on whether you are basing the new model on a previous model or not. If you are developing a 'new and improved' version of a previous model, often you would start by taking note of all the phone's most successful features. For example: Good battery placement/life, ease of keypad use, often used features such as speakerphone or notepad etc. Despite taking these all into account, it's possible that the new phone will not resemble the previous phone at all. There are a number of reasons a manufacturer might want to launch a new 'look' for a new model of phone - the previous one proved less popular than hoped, new technology (ie touch screen) has become more easily available and affordable etc.
If you are designing a new model of phone and it's not based on a previous model, research would most likely begin with analysing the most popular handsets on the market at present and determining which features/qualities are their biggest selling features. Then, working from this basic template, the new model in development would ideally have a unique selling feature that none of these analysed phones already possesses.
If you are designing a new model of phone and it's not based on a previous model, research would most likely begin with analysing the most popular handsets on the market at present and determining which features/qualities are their biggest selling features. Then, working from this basic template, the new model in development would ideally have a unique selling feature that none of these analysed phones already possesses.