A Featureline is no different to a regular phone line except that it gives you access to a whole load of calling features within BT's exchange software which allows you to configure a group of lines as if they were a private branch exchange, or just to get some of those features on a single line. That means that Featureline won't of itself prevent a third party ADSL service being delivered over the line, including where the lines are part of a hunt group. It will be interesting to see what BT or your alternative supplier say about it.
