I tried to compile chan_capi-0.3.5 with the patch from April 05, but i got errors in other files. Here is a patch which applies clean and fixes all files. The only thing needed is to copy channel_pvt.h from asterisk-1.0.* to /usr/include/asterisk/
Here is the patch:
It seems that with a Fritz, it cancels better echo than newer versions. I got it working correctly with asterisk 1.2.4.