Codewalkers.com has this new tutorial posted today, introducing you to how you can use PHP to send SMS via HTTP.

SMS (also known as text-messaging) has grown into a very popular method of communication. It has been around in Europe and Asia since the early nineties and its use is steadily increasing in the US as well.

[...] Although this tutorial can be used for any gateway that provides access via HTTP, it is based on TM4B's SMS Gateway because A) they are the only gateway I know that have a simulation mode for tweaking your scripts, B) they don't have any set-up fees, C) their prices are low, D) they are reliable and E) I use them.

He shows you what SMS is, how it can be useful, and, of course, how you can send the messages (with both sockets and cURL).