What ports should I open on my firewall for H323 and SIP calls?

The receive ports used for RTP start at 1024 and can be any even port number above that - RTCP uses the odd numbered ports. There is no control over the port that is used for a particular call. The port that the card sends its RTP to is specified by the far end during call set up. According to the SIP and H323 specs, this should always be equal to or above 1024.