Amazon says it's replacing free two-day shipping with free one-day shipping for its Prime members. Amazon's chief financial officer made the announcement during the company's first-quarter earnings call. No date was announced for the launch, but the CFO said it will take "a significant amount of time" to achieve. Amazon plans to spend 800-million dollars in the next quarter to make the transition, to improve warehouses and delivery. Because of the large investment, Amazon predicts its earnings will drop belows expectations next quarter. Prime members already get one-day shipping for certain products. Amazon says it will make it the rule and not the exception.