1. Plug in the modem 
2. Open a terminal and login to the root user account (use the command su).
3. Execute the command:

# lsusb

4. Output will be something like:

Bus 007 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 006 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 003: ID 1131:1001 Integrated System Solution Corp. KY-BT100 Bluetooth Adapter
Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 002: ID 05c6:6000 Qualcomm, Inc.
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

The second last line is what we are interested in:

Bus 003 Device 002: ID 05c6:6000 Qualcomm, Inc

The modem manufacturer is Qualcomm Inc. Note the USB device corresponding to it.
Here, 05c6 (in hexadecimal) is the Vendor ID and 6000 (again n hexadecimal) is the product ID. Note them down.

5. Execute the command:

# modprobe usbserial vendor=0x05c6 product=0x6000

The command is in the format:

# modprove usbserial vendor=0x<your_vendor_id> product=0x<your_product_id>

6. Execute the command:

# cd /dev# ls ttyUSB*


If there is a device with name ttyUSB0 then the modem has been recognized. Else, retry the above steps.

7. To configure the the dialler(the wvdial dialler is used), execute the command:

# wvdialconf /etc/wvdial.conf

NOTE: This command will work only if the wvdial is already installed. This dialler is part of most Linux distros (mandriva, ubuntu, fedora or openSUSE etc). If wvdial is not present, there should be some other dialler like kppp installed.

A file wvdial.conf will be created in the /etc directory. Execute the command to edit it:

For KDE users

# kwrite /etc/wvdial.conf

For Gnome Users

# gedit /etc/wvdial.conf

Change the file contents to:

[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem = /dev/ttyUSB0
Phone = #777
Idle Seconds = 7200
Modem Type = Analog Modem
Stupid Mode = 1
Compuserve = 0
Baud = 921600
Auto DNS = 1
Dial Command = ATDT
Ask Password = 0
ISDN = 0
Password = 
Username = 

For example, if the username and password are 1234567 & 1234, then the file would look like:

[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem = /dev/ttyUSB0
Phone = #777
Idle Seconds = 7200
Modem Type = Analog Modem
Stupid Mode = 1
Compuserve = 0
Baud = 921600
Auto DNS = 1
Dial Command = ATDT
Ask Password = 0
ISDN = 0
Password = 1234567
Username = 1234

8. Execute the command to dial up and connect to the internet:

# wvdial

DO not close the window as it would close the connection(better minimize it). And when you need to disconnect, press CTRL + C inside the window.
In case of problem, just add comment to this blog or mail me with the problem.