EBay has agreed to buy the fast-growing internet start-up Skype in a move to add free web telephone calls to its online auctions and fuel growth, the companies confirmed on Monday. EBay plans to pay .3bn in cash and .3bn in stock for the web communications company. It will make a further payout of up to .5bn by ’08 or ’09 if financial targets are met, giving the deal a total value of up to .1bn, executives of the two companies said. EBay is renowned for an internet business model linking millions of buyers and sellers, but its core US market is maturing, slowing to annual growth of 20-30% a year against a 50% global growth.