Today's top Apple(AAPL) stories include another prepaid iPhone, and a report that Apple is dropping the limit on iPad purchases. Virgin Mobile USA, the prepaid division of Sprint(S) , will start selling the iPhone 4 and iPhone 4S at the end of this month. Virgin Mobile becomes the second prepaid carrier to start selling Apple's smartphone. It will sell the 8 GB iPhone 4 for $549, and the 16 GB iPhone 4S for $649. The unlimited data and messaging plan starts as low as $30 per month.