For QCDM devices we want most of what MMSerialPort does, but not
the AT command handling stuff since the commands and responses
aren't AT commands nor are they even strings. So convert everything
that MMSerialPort does into a GByteArray, and let MMAtSerialPort
handle the conversion to strings when necessary.
Like UMTS vs. GSM, EVDO and 1x are separate networks and technologies
and have separate registration state. You can even be roaming on
EVDO while in your home 1x network. Handle that.