PHP Automatic SMS Scheduler enables you to send mobile sms to people on an exact specified date & time automatically.
The installation is very easy WordPress like!
A ) A doctor might want to send an automatic scheduled SMS to remind a patient about his appointment.
B ) A car service could remind when the service is due automatically.
C ) A company might want to send happy birthday sms to a customer automatically.
This script requires either clickatell.com OR experttexting.com SMS GATEWAY which charges based on each country/operator. You will need to purchase a credits package before being able to send any messages.
Check pricing & coverage for clickatell: http://www.clickatell.com/pricing-and-coverage/message-pricing/
Check pricing & coverage for experttexting: http://www.experttexting.com/pricing/