I've seen many SMS sending services such as http://sendible.com/ where they offer plans on sending sms messages out. I'm interested in knowing exactly how they send out messages from a server? I want to develop my own sms sending software but I dont know how to actually get the service that sends out the texts that I can integrate into the software. Please help?
they are using sms gateways, there are some open source absolutely free applications for you. just google em.
You will need a SMS gateway. It's a company/website/whatever that you pay for sending SMS'es using their service. The price and the limitations are usually depends upon which country you reside in.. Use google to find gateways in your country. Good luck!