TORONTO: The National Post posted an apology on its Web site after a Twitter exchange between one of its reporters and a communications exec turned nasty.

The exchange erupted after April Dunford, founder of Rocket Launch Marketing, failed to call back technology reporter, David George-Cosh, for a story on time. Dunford posted a tweet that read: “Reporter to me ‘When the media calls you, you jump, OK!?' Why, when you called me and I'm not selling? Newspapers will get ...