Carphone Warehouse and Dixons Retail have won extra time to thrash out a potential merger, but speculation has emerged that Carphone's rival Phones4u may make a counter-bid.Mobile phone retailer Carphone and Dixons, which owns electrical and computer retailers Currys and PC World, have asked Britain's Takeover Panel to extend a deadline for making an offer from end of business on Monday to 17:00 on May 19th.A joint statement from the two companies said: "Since the announcement of February 24th 2014 was made, when discussions were at a very preliminary stage, both parties have agreed that they require more time to evaluate a potential merger of the two businesses."However, Britain's Sky News has reported that Phones 4u, which has a deal with Dixons to sell mobile phones in 160 of its Currys and PC World shops, has approached Dixons about an alternative merger deal.Entrepreneur John Caudwell launched Phones4u in 1996, but private equity firm BC Partners bought it in April 2011.Dixons and Carphone Warehouse announced last month they were in talks that could lead to a merger, although it has not yet been determined whether the deal would be a 50/50 merger or a takeover by one company of the other.Shares in Carphone fell 17.2p or 5.1% to 322.1p by 15:37 in London while Dixons' shares pared earlier losses to rise 0.3p to 50.2p.PW