Further AT commands

While some AT commands work on all devices, each vendor does seem to have a subset of commands

Some devices allow to poll signal quality with "AT+CSQ" (of course only if the modem port is not busy)

Some devices need to have the connection mode set via "AT_OPSYS="1,2" (or 2,2 etc.)

Some devices (Option and Sony Ericsson among them) need to have the phone functionality set first via "AT+CFUN=1,1" (turn flight mode off, etc.)

Some devices don't like to have the SIM authenticated more than once

Try to find the AT reference for your device and send them to me