How can I send a SMS text message to multiple recipients?

UPDATE: Send SMS or MMS messages to multiple recipients by adding them all to the "To:" line when creating a new message. Phone numbers can be entered and separated using the "return" key. Multiple recipients can be added from your Contacts using the "+" button.

Update (12/28/2007): Using a new third-party application for the iPhone, iSMS (or weiSMS), it is now possible to send text messages to multiple individuals as well as forward text messages. Find out more here.

The native iPhone SMS interface, as of firmware 1.1.2, does not provide the ability to send SMS text messages to multiple recipients (bulk SMS).