messagingtoolkit

There are plenty

• mcore SMS library at http://logixmobile.com, available as .NET dll or ActiveX component.
• jSMS from http://www.objectxp.com/en/products/jsms/, written in Java.
• ActiveExperts SMS and MMS Toolkit at http://www.activexperts.com/xmstoolkit/. It supports MMS also.
• Ozeki NG SMS Gateway at http://www.ozekisms.com
• SendXMS at https://www.bai.de/en/sendxms.shtml