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
Disabling PIN on SIM is easy: AT+CLCK="SC",0,"XXXX"

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