Supportive text messages can double the chance of someone successfully quitting smoking, according to UK researchers.
Just over 10% of 2,900 smokers who received encouraging texts such as "you can do it" had quit after six months, but only 4.9% of a similar number who did not have the same support gave up.
The study, published in The Lancet, called for texts to be included in services to help people kick the habit.
Other scientists said a text service could be offered globally.
According to government statistics two-thirds of UK smokers say they want to stop.
This study looked at 5,800 of them. Supportive texts were sent to 2,915 of the smokers for six months. The rest received only messages thanking them for taking part.
They were sent five texts a day for the first five weeks and then three a week for the next 26 weeks.
Participants could also text back for specific advice when they had cravings or had lapsed back into smoking.
Saliva tests for cotinine, which is made when nicotine is broken down by the body, were taken to determine if people had really given up.
After six months, 10.7% of those receiving texts had quit - double the proportion among those doing it on their own.
Dr Caroline Free, who led the txt2stop trial at the London School of Hygiene and Tropical Medicine, said: "Text messages are a very convenient way for smokers to receive support to quit.
"People described txt2stop as being like having a friend encouraging them or an angel on their shoulder.
"It helped people resist the temptation to smoke."
The World Health Organization says nearly six million die each year because of smoking, mostly in low and middle-income countries.
Dr Derrick Bennett and Dr Jonathan Emberson, both from the University of Oxford, said text messages could be used to help people around the world.
"The lessons learned from the txt2stop trial could... not only provide a new approach to cessation in high-income and middle-income countries, but could also provide a useful starting point for implementing behavioural change in resource-poor settings."
It has also been suggested similar text messages could be used to help people modify other behaviour.