There were 5.4 million phones active on the Nextel network at the end of March. Many Nextel customers are businesses or government agencies who issue the phones to construction crews and other mobile workers. Sprint now faces the challenge of convincing these customers to move to the Sprint network rather than competing carriers. As part of the pitch, Sprint has added phones with a walkie-talkie-like "push-to-talk" feature.
Sprint is deactivating the Nextel network to make room on the airwaves for a new fourth-generation, or "4G" data network. The Nextel network is a second-generation, or 2G, technology with low data speeds that are unsuitable for smartphones."
Link to Original Source