It's best to open all UDP ports (0-65535) for RTSP/RTP streaming. On the incoming side, the Wowza media server software tries to use ports in the range 6970-9999. On the outgoing side, the port choice is made by the receiving device so it's best to open all ports to outgoing UDP traffic. Setting up UDP networking correctly is sometimes difficult and depends on your router and firewall configuration. If behind NAT (network address translation), it's important that all UDP ports are mapped to the server running the Wowza media server software.
Wowza provides a RTSP/RTP test stream running on Amazon EC2, which seems to work on most mobile networks/devices. Amazon EC2 is a great place to experiment with RTSP/RTP streaming. For more information, see Wowza for Amazon EC2.
Some carriers don't allow RTP or UDP over the carrier network. Many mobile devices will rollover to RTSP/RTP interleaved (RTP over TCP). These devices will work when the carrier doesn't support UDP. Some devices don't support RTSP/RTP interleaved and won't work if RTP or UDP is blocked by the carrier. Use the RTSP/RTP test stream to see if it works first before setting up your streams.