Forwarding of SMS messages is a built-in feature for iPhones using firmware 3.0 or higher, so you can simply hit the button and send them on their way!
1) view the SMS text message conversation containing the message you’d like to forward
2) tap EDIT at the top of the screen
3) check off the message(s) you’d like to forward
4) tap FORWARD at the bottom right of the screen
There’s an app for that! If you’re using older firmware, there is a third-party application on your iPhone iSMS (or weiSMS) which lets users text message multiple individuals and even forward their messages.