To successfully configure my Tata Indicom Plug2Surf Modem, what I did was,
1. Insert the modem, and then open the terminal and type,
varsha@varsha-laptop:~$ sudo wvdialconf
varsha@varsha-laptop:~$ sudo gedit /etc/wvdial.conf
Edit the file:
Phone = #777
Password = internet
Username = internet
I am not sure if any other username and password would work, because it did not really work for me.
3. Save the file and exit the editor.
In addition to what you have done above, add the name of your modem in the Network connections. For this, right-click the Network Icon on the top panel. Then, do the following.
1. Select the tab Mobile Broadband. Click Add.
2. Click Forward (take the default settings on the first page).
3. Select India and click Forward.
4. Select the appropriate provider (Tata Indicom Plug2Surf in my case). Select I can't find my provider and I wish to enter it manually if you don't find your provider in the list. Click Forward.
5. Click Apply.
6. Take the default #777 in the Number field, and enter internet (as you have edited the /etc/wvdial.conf file) in the Username and Password fields.
7. Connect automatically and Available to all users are optional.
8. Click Apply.
9. Select the name of your connection from the list and you will see that connection is established.