5.18.3.10. Tracing End-of-Dial Without Charges 
In some countries (such as Brazil), it should be possible to trace
an MFC end-of-dial without charges. (Extension of the possible B signals
when calling an available user.)
If a user has both the trace class of service and the 'without
taxation' class of service, use MFCTA as follows:
CHANGE-MFCTA: MFCVAR=x, TYPE=TBLB, OPT=BSIGB, EODTYPE=MCIDFC, BSIG=7;