How SMS Gateway works

[SMS]

In order to send SMS you need a SMS gateway. Those are easy to come by, as there are a few free ones you can download.

The problem comes when you want to connect the gateway to a cellular provider. Unless you own one of those fancy cell boards that the likes of Nokia and Motorolla produce, and cost quite a chunk of change, the means of connecting to the cell network is your cell phone (or if you can afford one, a cellular modem).

Depending on what plan you have, your cellphone may allow unlimited SMS, or ony x amount of SMS messages before they have to charge you.

Knowing these two things, all you need now is a cable to connect your cellphone to a computer (which will run the gateway server). You can then interface the server with your website and start your own SMS service.

Alot of the gateways come with APIs that you can use to integrate with internet-friendly languages (like PHP, ASP, VB, etc.)which enables you to write the "code" that will interface your website with the server.

Thats pretty much all there is to it.

The easiest way to provide "free" SMS services is to interface with the email options that providers like AT&T have. Basically, your application acts like a browser and takes the information from the user form, and plugs it into the form that (for example) AT&T provides and sends off the SMS. The underlying code is known only to you, and to the end user it seems like the SMS is being sent by your site. I know for a fact that each cell phone that AT&T gives out has an email address associated with it, so this is easy enough. For providers that are not GSM (like Sprint, which is CDMA) you'd have to go through their website and find options to send SMS (I'm sure they have a "Send SMS" form on their site that you can .. err ... integrate into yours).

You can provide free SMS services using the dedicated server option, but then you'd have to find a cellular provider that has a plan that allows for unlimited number of SMS messages per cycle.

[SMS]

http://www.visualtron.com.sg/products_vgsmlite.htm
http://www.kannel.org