I used this script for many years with some modifications, and it worked quite well for selling voip cards using btcvoip.com now dead due to market reasons, I still had this script on my server but it was stolen by Mexican police, when they into my place broke and did massive destruction.

Thanks for the script it really helped and overall it works well, one of the things I had to change was session timeout which was too low, especially now that bitcoin transactions take a long time, and some very minor changes.