How to send mass text messages to a 5 digit number?

Yeah there is a radio competition between a few schools around us to text this 5 digit number a message with your school name as many times as you can and the winner gets this artist to perform at the school.

Some of my friends have sent hundreds of text messages but I got the idea of using the internet to send free text messages.

Someone said they tried AIM but it would not work with a non 10 digit number.

So my question is what is the best way to send as many text messages using my computer as I can.

A program that does it would be nice.

The second problem is the 5 digit thing. Is there a way around it? Maybe if I can find the 10 digit number that it is linked to? But I dont know if I can do that.

Thanks.

Back to googling about it more.

edit: see here is a site that does it but only accepts 10 digit numbers

http://smseverywhere.com/send.htm