I had UHCI on my USB so i gave it a quick try.
I used this ztdummy-module and got scratched up sound from asterisk. (worked before)
With zaprtc it worked better however for all hardcore linuxers: You HAVE to execute the rtcsetup. I am not completely clear what it does but if you dont execute it asterisk will not respond. (asterisks scheduler will have no timing instead of a bad one :)
And if you get messages about missing symbols when loading one of the kernel modules you should do "lsmod" and look if the module is loaded. You find it in your sourcedirectory after compiling called "zaptel.o".