To describe the design and rationale of the NHLBI-sponsored Cell Phone Intervention for You ( CITY ) study , which is a single center , randomized three-arm trial that compares the impact on weight loss of 1 ) a behavioral intervention that is delivered almost entirely via cell phone technology ( Cell Phone group ) ; and 2 ) a behavioral intervention delivered mainly through monthly personal coaching calls enhanced by self-monitoring via cell phone ( Personal Coaching group ) , each compared to 3 ) a usual care , advice-only control condition .