Znisms is one of the largest Bulk SMS providers and aggragaters in India, and supplies a number of SMS services. The API suite offers :
HTTP SMS API (HTTP API based on REST) used to send single SMS from your application
Group SMS API (XML API) sending SMS in masses e.g. you have a messages which you want to send to 1000 people i.e. same message to multiple recipients.
Balance Check API and Delivery Report API
Dynamic XML API for sending customized SMS i.e. different numbers, different messages in masses.