Methods: In this single-blind, randomized trial, undertaken in China, about 2,000 smokers willing to make a quit attempt will be randomly allocated, using an independent telephone randomization system that includes a minimization algorithm balancing for sex (male, female), age (19-34 or >34 years), educational level (≤ or >12 years), and Fagerstrom score for nicotine addiction (≤5, >5), to 'Happy Quit', comprising motivational messages and behavioral-change support, or to a control group that receives text messages unrelated to quitting.