Does the iphone sdk support playing an mp4 from rtmp stream?

Please check the Wunder Radio application from iTunes. It is open source under LGPL license. The code is available from here - http://www.wunderradio.com/code.html

No. The iOS SDK does not support the RTSP protocol. You may be allowed to include an implementation of RTSP into your app, but Apple is strongly pushing their HTTP streaming technique. Also: beware of this rule from section 9.4 of the developer guidelines:

Video streaming content over a cellular network longer than 10 minutes must use HTTP Live Streaming and include a baseline 64 kbps audio-only HTTP Live stream

I believe everyone is using Apple's HTTP Streaming technology. It is the supported and blessed approach.