Shares in Sprint Nextel surged on Monday after the struggling third-largest US mobile phone company reported reduced operating losses and an unexpected per share profit excluding certain items, together with strong customer gains for its Boost Mobile pre-paid unit.

Sprint’s Boost Mobile unit, which introduced a new $50-a-month unlimited calling plan during the quarter, added 764,000 net new customers, highlighting the growing popularity of pre-paid mobile service in the US among consumers hurt by the recession.