There are many providers of SMS services out there. You normally pay a monthly fee for incoming traffic and then a fixed amount for example for every 1000 SMS you need to send.
Here is an example of one of them http://www.clickatell.com/ Note that I have never used them and don't recommend them in any way. You want to find a company operating in your local country.
Your second alternative is to get one of those 3G Data Modems and hook up to the server. Some of those modems provides an API to send and receive SMS. You will then need a fully working SIM, might be cheaper for lower volumes but slower and less stable solution usually.