1. Plug your modem on the computer.
2. Install wvdial in you terminal, by typing 'apt-get install wvdial' ... if you are connected with online/offline repositories,but if you are not connected then you must download the wvdial and dependencies then install it.
3. after installing, type 'wvdialconf ', and wait for the wvdial to check the existance of modem.
4. After finish the wvdialconf command,then you have to write 'gedit /etc/wvdial.conf ' .
5. Then write this to the wvdial.conf
[Dialer Defaults]
Modem = /dev/ttyUSB2
Baud = 1843200
Modem Type = Analog Modem
Init2 = ATZ
Init3 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Init4 = AT+CGDCONT=1,"IP","<write your apn here>"
Dial Command = ATDT
Phone = *99#
Username = <write your username>
Password = <write your password>
Stupid Mode = yes
6. Then save it, after all type 'wvdial' and Enter it.