My colleague Roberto is experimenting with Clickatell to send SMS messages from applications, with very good results. This looks like another "It Just Works" service.

The gateway is very well done - this is a perfect example that you don't need SOAP to make web services work, these guys allow you to use HTTP, mail, FTP (among other ways) to access their engine.

The fact that SMS sent via their services are much cheaper than using a local provider opens some interesting business perspectives...