Thank you for the reply, l have a general understanding and have written a php script to do the work.My problem comes on troubleshooting the link.If l don't get a response how can l confirm if USSD gateway is not sending back response or l am just not capturing it etc.
If you work with a local server, then you can use a tool like Fiddler to trap incoming/outgoing data. Next to that, add logging to everything you do, whether it's to file or database. If the USSD is not responding, it can be hardware and/or software. They should have a sandbox for you for testing purposes.