There are many SMS sending gateways that provide REST services to send SMS. You need to register and purchase credits first before SMS can be sent. One such gateway is ClickaTell:
Below is the sample REST call of Clickatell service provider:
Though this is only HTTP way, we have numerous ways to send the sms which include SMTP/Email to SMS, FTP API, SMPP, COM Object, SOAP API, HTTP/S API, XML.