First unofficial information came in last decade of 2011 from YAESU Amateur Radio (Vertex Standard Division). Company has developed new C4FM FDMA (4 FSK Level) mode for Amateur Radio.
See brochure screenshot below:
Please find more information in PDF brochure from YAESU.
Most likely in the near future YAESU will release new C4-FM Radio for the radio Amateurs. Let's wait month or two...
351.20000 ~ 351.38125MHz (between 6.25kHz, Wave 30)
351.16875 ~ 351.19375MHz; channel for the sky (between 6.25kHz, wave 5, reception only)
F1E, (FSK value of 4)
Simplex (Press Talk) method
(5 sent, 5 received 90 repeat standby)
FNB-V86LI · · · approximately 6.5 hours
FNB-11 hours V87LI · · · (battery...