General Motors Co on Feb. 1 will begin a $1,500-per-month on-demand concierge subscription service for Cadillac cars and SUVs in New York, a program it hopes will expand to major cities in the United States, Cadillac said on Thursday. GM and Cadillac will maintain a small fleet of Cadillac cars and Escalade SUVs to serve dozens of clients for the initial phase of the luxury service, which company executives hope will attract first-time drivers of GM's luxury models. Cadillac officials did not say when they expect BOOK by Cadillac to expand beyond the New York metro area.