A long time ago (4+ years) I used to have program to send SMS by connecting to mobile operator SMS server and sending it trough some wierd port. But after they found out people were abusing that for flooding and other not-so-nice things they blocked it. Not to mention you could do stuff like enter any source phone number, so you could send fake SMSes.

There still is a program called SmartSMS or something like that, that lets you send SMS trough different ways, even trough directly connecting to SMS server via analog modem :). To bad most of them have disabled this 'feature'.

Well, if someone has some code to send SMS trough some free webservice I would also really like to see it.

I've done a project some time ago for university (with two others). We'd connect to a cellphone through the serial port and receive/send SMS messages via the phone. The phone would receive an SMS, the computer would download and analyze it and send a new SMS to someone else depending on the contents.

I haven't done the connectivity part, but it's not too dificult. You should be able to find libraries to communicate through the comport, and a reference chart what commands to send to the phone. It's like 'talking' to a modem actually... 'AT+CMGF=0'

What I've done is encoding and decoding the SMS messages. Here's the page I used as reference. They're stored in PDU format. You can do a lot of interesting things like fake the senders number (since that's part of the message...)

I won't be able to show you the sources though, since it was done on behalf of a company, they wanted to relay service orders this way. The customer would send his incidents (in some number coded form) to a fixed number and the system would then re-send the order to whatever technician was currently available.