BOSTON – Cellphone companies say service is operating in the Boston area, but with heavy traffic following the explosions at the Boston Marathon. A law enforcement official, citing an intelligence briefing, said cellphone service had been shut down Monday in the Boston area to prevent any potential remote detonations of explosives. But officials with Verizon Wireless and Sprint Nextel said there had been no such requests. Sprint spokeswoman Crystal Davis said: "Minus some mild call blocking on our Boston network due to increased traffic, our service is operating normally." Two people were killed and scores injured when two explosives detonated near the finish line of the marathon.