Hi, This is just to share how we can find out which serial to be used with gsmopen Install wvdial : yum install wvdial then run : wvdialconf /etc/wvdial.conf It will display output like : Editing `/etc/wvdial.conf'. Scanning your serial ports for a modem. ttyS0<*1>: ATQ0 V1 E1 -- failed with 2400 baud, next try: 9600 baud ttyS0<*1>: ATQ0 V1 E1 -- failed with 9600 baud, next try: 115200 baud ttyS0<*1>: ATQ0 V1 E1 -- and failed too at 115200, giving up. ttyS1<*1>: ATQ0 V1 E1 -- failed with 2400 baud, next try: 9600 baud ttyS1<*1>: ATQ0 V1 E1 -- failed with 9600 baud, next try: 115200 baud ttyS1<*1>: ATQ0 V1 E1 -- and failed too at 115200, giving up. Modem Port Scan<*1>: S2 S3 WvModem<*1>: Cannot get information for serial port. ttyUSB3<*1>: ATQ0 V1 E1 -- OK ttyUSB3<*1>: ATQ0 V1 E1 Z -- OK ttyUSB3<*1>: ATQ0 V1 E1 S0=0 -- OK ttyUSB3<*1>: ATQ0 V1 E1 S0=0 &C1 -- OK ttyUSB3<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 -- OK ttyUSB3<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK ttyUSB3<*1>: Modem Identifier: ATI -- Manufacturer: huawei ttyUSB3<*1>: Speed 9600: AT -- OK ttyUSB3<*1>: Max speed is 9600; that should be safe. ttyUSB3<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK WvModem<*1>: Cannot get information for serial port. ttyUSB4<*1>: ATQ0 V1 E1 -- failed with 2400 baud, next try: 9600 baud ttyUSB4<*1>: ATQ0 V1 E1 -- failed with 9600 baud, next try: 9600 baud ttyUSB4<*1>: ATQ0 V1 E1 -- and failed too at 115200, giving up. WvModem<*1>: Cannot get information for serial port. ttyUSB5<*1>: ATQ0 V1 E1 -- failed with 2400 baud, next try: 9600 baud ttyUSB5<*1>: ATQ0 V1 E1 -- failed with 9600 baud, next try: 9600 baud ttyUSB5<*1>: ATQ0 V1 E1 -- and failed too at 115200, giving up. WvModem<*1>: Cannot get information for serial port. ttyUSB6<*1>: ATQ0 V1 E1 -- OK ttyUSB6<*1>: ATQ0 V1 E1 Z -- OK ttyUSB6<*1>: ATQ0 V1 E1 S0=0 -- OK ttyUSB6<*1>: ATQ0 V1 E1 S0=0 &C1 -- OK ttyUSB6<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 -- OK ttyUSB6<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK ttyUSB6<*1>: Modem Identifier: ATI -- Manufacturer: huawei ttyUSB6<*1>: Speed 9600: AT -- OK ttyUSB6<*1>: Max speed is 9600; that should be safe. ttyUSB6<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK Found a modem on /dev/ttyUSB3. Modem configuration written to /etc/wvdial.conf. ttyUSB3<Info>: Speed 9600; init "ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0" ttyUSB6<Info>: Speed 9600; init "ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0"