The SIM card is in the modem and the PIN code is disabled. S0 are set for something different than 0 and the modem seems to be answering, but it's only silence and nothing happens. A2 The number you are calling to the GSM modem is the normal voice number. When you want to use the GSM-modem for data communication you must have a special data number to the SIM card otherwise will not the GSM-modem understand that there is a data call coming in. To check if this is correct could be tested with the AT+CRC=1. The modem will then report the type of connection you get when there is a call coming in. It's sometimes possible to make a work around with the use of the AT+CSNS=4. With this command the modem will answer in data mode regardless of number that has been used. This is a feature that some operators have blocked. A special data number could be obtained from your operator.