Carphone Warehouse, Europe\'s biggest retailer of mobile phones, is to shut 11 loss-making electrical superstores and exit a north American joint venture, the company announced on Monday. \"We have undertaken a comprehensive strategic review,\" Carphone Warehouse chief executive Roger Taylor said in a statement. Carphone Warehouse said it had agreed to sell its stake in a joint venture operating mobile phone stores across Canada and the United States to partner Best Buy Co. for £838 million (977 million euros, $1.34 billion). It plans to return the bulk of the cash proceeds to shareholders, Carphone said in the statement. It added that its Best Buy Europe unit would close all of its 11 Best Buy electrical superstores in Britain whose combined losses widened to £46.7 million in the six months to September 30. Carphone said it hoped to find roles elsewhere within the organisation for the \"large majority\" of 1,100 staff employed by the Best Buy stores.