ITU-R M.584-2 says that the function bits should be 11 in the case of
alphanumeric messages, and 00 in the case of numeric messages.

The CCP-6000 accepts and displays messages regardless of the value set,
but puts them in the "PERSONAL" menu when functionbits == 11.  For now,
do what the spec says unless we have evidence that we should do
    otherwise or make it configurable.