It almost appears there is a problem initializing the modem, possibly wrong initialization strings.
This string of modem commands are a generic set of modem commands, I notice the errors relating to FCLASS, maybe you might want to play around with these settings. It could be all together different in China, but wouldn't hurt to try.
This string is usually produced by wvdial for init 2 string. Usually init 1 is ATZ, but this is also for analog modem, it could be different for voice modem.
ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Maybe search the net for init strings for your Rockwell, I put "voice modem init strings" in the Google search field and found too many results to list here. Might have to narrow it down to "Rockwell voice modem init strings". Because yours appears to be a 36k modem, this web page offered some possibly relevant info for Rockwell.
Maybe check the vgetty man pages for this -->modem quirks: 0004