China mnufacturers produce more and more phones with PTT - FM walkie talkie module 400...480 MHz band or(and) 130...180 MHz band, working trongh serial port. But it power management realized by two methods - direct GPIO management from JNI or IOCTL management of device. But all that methods are hard to create different software for PTT - because it does not have a special API in android platform.
Phones with PTT:
and more ...
It is very important that all these devices were in line with what a standard. And in the firmware was "API", which allows you to work with the radio module regardless of the manufacturer and firmware version.
I hope that the people involved in the development drivers will notice this topic.