SMS stands for short messaging service. This service is available in almost all digital mobile phones, pocket PC or even desktop https://www.learn-basics.com/computers which allows for short messages to mobile phones or even landline phones. Communication can be done through SMS via text messages such as ordering products, chatting, participating in contests. There are also many services available on internet which allows users to text messages.
Originally SMS was designed as a part of GSM but now is available on a wide range of networks. SMS is more popular in India as companies provide low charges on SMS and entertain youngsters as they often exchange lots of text messages.