The first step:

Preparation

Find out which phone company supplies your building:

• TOT numbers:     In Bangkok numbers start with 2, 3, 4 or 5  ex: 02-2...
• TRUE numbers:  Numbers start with 6, 7, 8 or 9.                      ex: 02-6...

If you don’t know your telephone number ask your landlord, or call your mobile phone number and see what phone number shows up on the screen.
In case you have a number with an extension you might have to dial 9 first to get a dial tone.
If you already have a direct line continue with step 3

The second step:

The Telephone Line

If you have a number with an extension you will have to contact the landlord to get your own line.
(In Thailand the landlord is owner of the telephone line and not the tenant)

Talk to the management of your Apartment and tell them that you want to apply for ADSL. (They might have a spare line for you to rent or they need to agree that a telephone company provides you with a new line).

If you don't have a telephone line yet you can contact any telephone company you wish.
In Bangkok either TRUE , TOT or BuddyBB.

The third step:

High Speed Internet

In Thailand you usually have to choose the ADSL Line from your telephone company.
If you want to choose a different company to provide you with ADSL it's more expensive

To apply for broadband Internet you may need:

1. Photocopy of your passport  and valid non Immigrant B Visa , which you must sign
2. Photocopy of the last lease contract  (which links the property to you)
3. Photocopy of the House Registration Document (Tabien Baan)
   (showing who owns the property that the service is being provided for)
4. Photocopy of the Landlords ID card, which he  must sign