this may be very difficult to do with Apple iPhones because their SMS API locks this ability. It's even locked within Android Phones to 100 outgoing SMS Messages per hour.
That being said there's always a way around. You will need to install Cydia on your iPhone, and for your Android you will need to http://www.market4android.com/how-to-remove-the-100-sms-limit-each-hour.php
Then you will need some sort of Bulk SMS Software which handles incoming and outgoing message management. If you are looking for one where there's no per sms cost, and which will work with your smart phone (Android OS) or a simple phone then I would check out http://www.firetext.com, for Apple, just do a search within the Cydia store for SMS.