With iPhone OS version 3.0 or later, iPhone is capable of receiving streaming audio and video over HTTP from an ordinary web server. Because the system uses HTTP, it is supported by nearly all edge servers, media distributors, caching systems, routers, and firewalls. To support content providers who wish to protect their media, the streaming system provides for media encryption and user authentication over HTTPS.
Apple: HTTP Live Streaming Overview

Also there are lots of streaming servers that you can use to broadcast content. For example, you can use Wowza Media Server can stream to iPhone and iPod:
Wowza Media Server: Secure streaming to the iPhone and iPod Touch