when you first get connected to your specially subsidised install and supply, you are contracted to the phone line for the first 12 months only with a standard box . sky plus and Hd are different in that they insist it be connected all the time.
I am an independent sky installer and in the early days they were quite slack on authorisng by phone,just get people connected !! however it has become more difficult to take that short cut to the point that they will not 95% of the time connect the card without a callbacK which is a real pain.
As someone else advised , the best way is to put in some temporary phone extension in before the instal date and tell the installer that BT are putting a line in tomorrow or something.
As someone who fits these things I can sypathise as sometimes it takes what seems like forever to get a successful callback.
the other dodge is to get the one for all wireless telephone extension kit ( no wires) but they are about �60 a pair but do the job in an instant.