how to make incoming sms free using sms gateway in my website

i'm planning to build a website which will interact with SMS sent from mobile numbers.i know that various sms gateways are available that can be used.But i want the incomming SMS to be free of cost. i.e. the SMS that will be recieved by my application will be free of cost irrespective of sender number.How can it be done.Please give me some solution.