A MTP can bridge tohether two full-duplex voice stram and if necessary convert between G711 ulaw and alaw as well as different sample sizes. So as the MTP bridge is handling each stream independently, H.323 supplementary services can be supported. In other words, MTP will enhance H.323v1 with all these supplementary services(Call Park, Hold , Transfer , Conferencing,…).
Pay attention also that you can use MTP in order to provide the translation between the out-of-band DTMF tones used by SCCP and SIP in-band (payload type) DTMF tones.