D-Star with Siemens C5 (former Cellphone)

Last weeks i tested D-Star. Jan Alte, DO1FJN developed a digital voice modem PCB which can be mounted to the C5 cellphone from Siemens. The modem firmware and the user software that runs on the phone┬┤s microcontroller is still in development but it does quite well already. I made a qso via the repeater DM0MW in Mittweida and also a direct qso with Peter, DL5DTL here in Dresden.
Overall the voice quality of the AMBE codec used in D-Star is not satisfying and FM sounds much better at the same signal level. The advantage of D-Star seems to be that you can carry data while doing a voice qso and you can receive a data channel on a repeater frequency. But is it worth investing the money for that ?
Anyway the modem from Jan is really impressive because the firmware is open source and it features a AVR32 microcontroller as well as an CPLD which enables to implement also other standards like APCO25, POCSAG or Packet Radio on it. Sounds it can be an interesting platform for implementing new ideas.