I don't have time now :-( but someone with a little time can just watch inside oslec zaptel patch and try to port to misdn; the core routine seems "echo_can_update" and it seems we just need to add the OSLEC version in place of one of the old ones:
mercurius:/usr/src/asterisk/CORE-1.4/mISDN-1_1_5# grep -r echo_can_update .
./drivers/isdn/hardware/mISDN/dsp_mg2ec.h:static inline short echo_can_update(struct echo_can_state *ec, short iref, short isig) ./drivers/isdn/hardware/mISDN/dsp_mec2.h:static inline short echo_can_update(struct echo_can_state *ec, short iref, short isig) { ./drivers/isdn/hardware/mISDN/dsp_kb1ec.h:static inline short echo_can_update(struct echo_can_state *ec, short iref, short isig) ./drivers/isdn/hardware/mISDN/dsp_cancel.c: rxlin = echo_can_update(ss->ec, txlin, rxlin);
Binary file ./drivers/isdn/hardware/mISDN/dsp_cancel.o matches
Binary file ./drivers/isdn/hardware/mISDN/mISDN_dsp.o matches
Binary file ./drivers/isdn/hardware/mISDN/mISDN_dsp.ko matches