Clickatell is a SMS gateway and also provide api like REST , http and https to send the SMS, below is the url of the clickatell site :
https://www.clickatell.com/test-sms-gateway/[
^]
They have also shared the example of how to use the api, click on API&Scripts link you will get the example. for example below http link you can call using java program:
http:
code
NOTE: You need to signup as a developer to get the 10 free SMS. Upon signup it will provide you the username, password and appid.