How I can Access FON1 analogue phone port so I can output some Audio via a C or Bash scripts/software on Frtizbox 7360?

What I want is using some shell scripts or a custom C software to access the FON1 port and log key presses. My router is a Frtizbox 7360 and using and accorting the device page in wiki FXS seem to be supported.

So in /dev/ there are the following devices:

bus              mei_cpe          mtd4ro           mtdblock5        ttyLTQ0          vmmc17
console          mtd0             mtd5             mtdblock6        ubi_ctrl         vmmc18
cpu_dma_latency  mtd0ro           mtd5ro           null             urandom          watchdog
dsl_cpe_api0     mtd1             mtd6             port             vmmc10           watchdog0
full             mtd1ro           mtd6ro           ppp              vmmc11           zero
gpiochip0        mtd2             mtdblock0        ptmx             vmmc12
gptu             mtd2ro           mtdblock1        pts              vmmc13
hwrng            mtd3             mtdblock2        random           vmmc14
kmsg             mtd3ro           mtdblock3        shm              vmmc15
log              mtd4             mtdblock4        tty              vmmc16

Which of the one above is the one that FON1 port uses in Frtizbox 7360?

What I want to do is a simpler-to-configure SIP client that directs audio from/to sip into this port.