I think that isn't too easy. To install the avm fritz + capi you have to recompile the kernel with isdn + capi support, then get closed source fritz capi modules from ftp.avm.de , rebuild them to suit the kernel in ASL and run. plus other capi utilities...
Perhaps the best way to do remote monitoring (oob) could be a remote managment hw like cyclades one.
Well, it is quite easy. the only thing i did was getting the pluspack, compiling the new kernel with isdn/avmb1 support, getting the fcpci-xxx.tar.gz from avm and the capi4linux drivers. compiled the fcpci driver, installed mtg-capri server, and thats it.