sysmoBTS + NITB

I have FINALLY gotten to play with my sysmoBTS acquired many months ago, and updated to the latest packages using okpg, and am running a NITB. GSM850 test setup in open mode A5/0, and I can SMS and call between devices. However, there is no audio, and BTS console logs reports many repeats of the following during an established call. <0006> tch.c:601 (bts=0,trx=0,ts=7,ss=0) Rx Payload Type EFR is unsupported <0006> tch.c:601 (bts=0,trx=0,ts=7,ss=0) Rx Payload Type EFR is unsupported <0006> tch.c:601 (bts=0,trx=0,ts=7,ss=0) Rx Payload Type EFR is unsupported