Guggenheim analyst Shing Yin said that Apple (NASDAQ:AAPL) may be open to a prepaid iPhone, iPhone 4 likely first.The iPhone 4 is likely to take the place of the 3GS, and the 4S will likley replace the 4 when Apple launches the iPhone 5 later this year.MetroPCS (NYSE:PCS) and Leap Wireless (NASDAQ:LEAP) could offer a prepaid iPhone 4 for $200 at retail, after $150 subsidy.Guggenheim rates PCS with a neutral and LEAP with a buy.