The above question may arise in our mind, because WhatsApp is gaining popularity around smartphone users. Just look at the fact sheet:

WhatsApp and SMS fact sheet



Cost Fact
To use WhatsApp you need a Smartphone and download this app. WhatsApp Android app download size is 12MB and that deducts from your mobile balance. SMS comes as in-built service in mobile phone
Do you know? WhatsApp is not at all FREE service. This service is a trial application and FREE for 1 year and after that you need to pay $0.99 USD/year to continue its usage. So, after 1 year your monthly cost to retain this app will cost you $0.99 USD/ 12 month = $0.0825 USD ? Rs. 5.13 INR (in Indian currency) To retain SMS service you don’t need to pay any money. It deducts money while send you SMS to someone
To send a simple message it cost you around 0.58 INR (approx) To send a normal text SMS cost you Rs. 1 INR for Local, Rs. 1.5 for National and Rs. 5 for International

If you have any inputs just let your comment on it.