If you are requesting an ADSL service then this is specific to the physical line it has been placed on, this is the same with any ISP unfortunately. You could use the other aspects of your service, such as email and webspace from different locations but not the actual ADSL connection.

I would like to join PlusNet but, before doing so, could someone please tell me whether I could use my PlusNet account at more than my home location e.g. when I am visiting family, or am I restricted to the BT phone number where I join.