TORONTO (Reuters) - Canada's biggest phone company has apologized after a punk-rock reference to the Holocaust appeared on billboard advertisements for its cellphones. The ads for Bell Canada's Solo discount service showed a young woman decked out in flashy punk rock attire, with a button that reads "Belsen was a gas" -- the controversial title of a song by the Sex Pistols, and a reference to Nazi Germany's Bergen-Belsen concentration camp. "It was inadvertent," Bell Canada spokesman Mark Langton said on Friday, noting that the dozen ads were taken down as soon as the company realized its mistake. "Obviously, we...