We support Bulk SMS. The API remains the same as sending a single SMS, as given here: How to send an SMS.
Send Bulk SMS With Static Content (refer this)
To send bulk sms, specify an array of "To" numbers instead of a single number. The API contract remains the same.
Sample PHP bulk sms API code sample is present at: Sample Bulk Code
Send Bulk SMS With Dynamic Content (refer this)
This API will send SMSes to different numbers with different message content for each number.