The latest data from Comscore regarding the United States smartphone market isn’t great for Microsoft. The company’s Windows Phone platform managed no growth, ending the May period with a 3 month market share average of 3.4%, the same level that Comscore reported for the platform in February. Android was flat, Apple picked up 0.6%, and Blackberry lost 0.6%. Android and Apple, however, control nearly the entire United States market, so to see little motion from them is hardly surprising. For Microsoft, which has invested billions into its mobile strategy, maintaining market share isn’t enough — it needs to grow. Microsoft has seen some international success with Windows Phone, but given the importance of the United States market in terms of developer density, the company can’t afford to neglect its backyard. Microsoft recently announced an OEM kit that may increase support for its mobile platform.