Accessing (the i4b) device driver

[Martin Moeller]

Hi all,

I'm totally new to FreeBSD programming, so please forgive my troll-like
question! I'd like to write a nifty little program showing if somebody is
calling me via an ISDN line. In the far future, the program should show the
caller's telephone number.
The ISDN kernel options are set and compiled ok, the system comes up with

isic0: <ELSA MicroLink ISDN/PCI> port 0xb800-0xb803,0xd000-0xd07f mem
0xeb800000-0xeb80007f irq 9 at device 11.0 on pci2
isic0: passive stack unit 0

so I assume everything's working great so far. 

I've looked around in /usr/src/sys/i386/include/i4b_ioctl.h and other files
but - to be honest - I don't have a clue how to go on from here. This kernel
stuff seems to be more complicated than the usual little useless programs I
write. :-(
Could you please point me to some documentation that is helpful? Nothing in
the FBSD developer/architecture handbook was able to enlighten me.

Thanks in advance!
Martin