From "MH370_Considerations on defining_FactSheet.pdf" (ATSB 26 May):
The final ACARS transmission was at 17:07 UTC and provided location reports from the initial stage of the flight as well as a recording of the aircraft fuel remaining.
And from ""MH370 Data Communication Logs.pdf":
All the transmissions (RX and TX) between 7/03/2014 17:06:49.406 and 7/03/2014 17:07:46.905 (pages 30 to 36).
The fact that channels are assigned and user data acknowledged implies that the communication(s) were established. The SATCOM use and the known ACARS timing published are in same minute. So, my understanding is the data transmitted via SATCOM were, at least part of them, ACARS.
And voice by SATCOM use C channel.
But I can be wrong!