We are developing a real estate site that gathers leads for multiple agents. We want to send SMS alerts to the individual agents when they get a lead and we want them to be able to reply with a short SMS back to our site telling us whether they want to accept or reject the lead. We then need to tie those responses into our database (MySQL, PHP). I am hoping there is a free script or system for this and, if not, can someone please direct us to the best gateway with the lowest fees. These SMS will be going only to US recipients.