Pitney Bowes' decision last December to spin off its office services business as a new company called Imagistic International seemed like an obvious way to dump a dog of a division. Earnings at the unit - which rents, sells and services fax machines and copiers- had slipped for three years straight, and growth prospects didn't look promising. The new stock lost a quarter of its value in its first week of trading. Since then, however, Imagistic has staged a turnaround.