I've written an app that I use for my own business. The application 'SMS Respond' replies automatically to SMS messages with a response message dependent on keyword.
I've tested it successfully with a couple of Samsung mobile phones, but it should work with any mobile that has a use a modem facility or a USB GSM modem.
If anyone want to test it, I would be appreciative of any comments. The trial allows short messages only, so send me an email for an unlock code if you get that far.
Many thanks,
Ed
http://www.smsrespond.com/
