By default Samsung will play a generated ring tone instead of the early media sent by Clearfly. There is an option in MMC210 that is called Real Ringback tone that can be changed by setting the "Real Ringback" value to "ON" in section 5.2.18 of the PBX configuration.

There is a known issue in which a Samsung will include a duplicate codec entry for G.729 in their SDP. This will cause the call to be rejected by Clearfly's SBC with a CANCEL message.