I have a solution for you already developed. I am USA based and have telephone and IM support
we use macro express on our RemoteDSL and ProxyDSL activated servers 2 ways to change the IP
1) pressing the F12 key (and the system will run a script accessing the router and resetting the IP address)
2) running a .bat file (and the system will run a script accessing the router and resetting the IP address)
We give you both solutions.
Also our script records your ip address and saves it to a file for later review, also if the script changes IP but ATT does not give you a different one, it will reset until it gets a different one. (sometimes ATT hands back the same IP if thier DNS server is busy)
Requires a dlink wireless router wbr2310 for fast IP switching (5-30 seconds) and your existing modem.
We will sell you the script and install it remotely on a windows compatible computer