OwenR is quite right in the settings described.

Now let me tell you what it means that BT don't support it. There are two reasons why they say they won't support it.

1. They'd like people who want to share their connection to buy one of their business packages and their equipment they re-sell as Owen suggests

2. They don't want their support staff to provide advice on kit not provided by BT

You can see their point with the second one. Would you want to train every helpdesk employee in every ADSL router known to man?

The upshot is that it will work just fine but if you have a problem getting it to work you can't phone BT for advice. However, you may get lucky and some kind sole on helpdesk will give you a clue but they reserve the right to turn around and say, "Sorry you're not running our supported hardware". More importantly you are not in breach of contract by using your own hardware.