If you actually want to send the SMS to the phone yourself, you'll need SMSC hardware connected to the server - I think it's more than a bit complex.
The simplewire setup will cost you $300USD + $57USD per 1000 credits and $50USD per support incident, or $400USD for the kit. This is probably pretty cheap compared with you'd spend in hardware setting up your own.
Most mobile companies charge to receive messages from other networks, so don't think setting up your own hardware will get you free SMS. (The reason they started charging each other was to (successfully) kill off all of the free services on the web, which can't receive and therefore couldn't charge, so had to quit as banners didn't cover the costs).