To compile you need a the gcc-avr toolchain and standard make utilities.
On Ubuntu/Debian this can be installed with:

apt-get install build-essential gcc-avr avr-libc binutils-avr avrdude

After that execute "make" in the main directory, and the modem firmware should compile.

You can use avrdude to flash to an Arduino compatible board. Have a look at the "flash" script, it makes this easy. If your board is connected to /dev/ttyUSB0, simply run:

./flash USB0

And avrdude should upload the firmware to the board.