If you have an ISDN telephone line, there is a process for having your line converted to ADSL. When you start the signup process for Topletter broadband you will need to enter the telephone number that you would like ADSL installed on. In the case of ISDN conversions, this will also determine which of your telephone numbers is retained. Please note the ISDN product you have will determine which of your ISDN numbers, you can choose from, see the table below for more information.

When ordering Topletter broadband, please ensure that you enter the correct telephone number in the 'Telephone Number' field on the 'about you' page. If you order your broadband service on a telephone number that cannot be retained, your order will be cancelled by BT. Likewise, we cannot accept responsibility if your ADSL service is delivered to the wrong ISDN number, if this is the number that was entered during the signup process.

An ISDN to ADSL conversion requires a BT engineer to visit the property, therefore you will need to ensure that access to the property is available during the appointment time. We will advise you of the appointment time in your welcome letter. If the appointment you receive is unsuitable, you must notify us at least 48 hours before the appointment time, else an administration fee may apply. If the BT engineer arrives at the site and is unable to start the conversion you may be charged an abortive visit fee of £58.75 inc VAT. On average, the appointment date will be 5-7 working days from the date of your order.

If the ISDN to ADSL conversion is unsuccessful, the BT engineer will return your telephone line back to its original state and your ADSL order will be cancelled. You will not be charged for the attempted installation.

If you have any queries regarding this process, please contact our customer services team. Their details can be found on the contact us page.