The very first thing we need is our computer/lap top should be equipped with a modem.So now remove your telephone line from phone device and connect it to modem on laptop.
Creating a new dail up connection in XP:(1)
Process with images

• Go to from Start menu- Control Panel
  
• Go to Network Connections On the left side, click on Create a new connection A window will appear.
• Click on the Next > button.
• Select the option Connect to the Internet and click on the Next > button.
• Select the option Set up my connection manually and click on the Next > button.
• Select the option Connect using a dial-up modem and click on the Next > button.
• Type in BSNL under the ISP Name and click on the Next > button.
• Type in the phone number that you will be using to connect to BSNL and click on the Next > button.
• Username: 8025717613(your telephone number without zero in the STDcode+yournumber - 80(080 is bangalore code- 25717613 is landline numeber)
• Password: 25717613(password would be your phone number)(Password is case-sensitive and should be comprised of alphanumeric characters.)
• Click on the option Add a shortcut to this connection to my desktop if you want to create a shortcut on the desktop.
•  Click on the Finish button. A new dialer is created in the Network Connections.
• A connection shortcut icon will appear at the Windows desktop.
•  You've successfully setup the BSNL Internet connection.
• Now right click on short cut created on desk top with name BSNL and say connect ...here you go ...It should work.

Note : It is a free service from BSNL , but you have to pay for the local call telephone charges for the duration of your Internet usage.
Problems in Dial up connection:Some times this process will not help to connect to the Internet so there are small things to be taken care while creating the connection, those are as follows.

• Right click on your short-cut go to Properties. General Tab.
• There is a drop down menu for selecting our country, Select India(91) .
• Just below the drop down check the check box with name "use dialing rules"
  Now just beside check beside you find a button with name "Dialing Rules"
• Click on Dialing RulesClick on new button and create a new location with ur are name and area code : ex : Bangalore 080After creating new location
• Try editing it using Edit button. In the edit screen verify your country to be as India (which ever you gave already)
• Make sure that the phone number to be dialed as should be shown as 172222
• Select Radio button "Pulse"
• Click ok in all the windows and now try connecting hope it should work this time.