I learned something today, when placing a home moving order with BT and you have your ADSL through someone else, like Be, it is important to mention terms like simultaneous provide early in the call. Your ADSL provider needs a linked order reference number or LORN to allow simultaneous provision to happen. That is you get a telephone line and at the same time you get ADSL service. However if you ask for a reference number (even specifying a linked order one) you often get a VOL011 order or BTCOM BT order number and not the LORN you need. When they submit the order it is not possible to then get a LORN number added to the order, it must be done before the order is placed.
So when calling BT on 0800 100 400 mention early in the call you have ADSL with another provider. Say you like to have simultaneous provide (sim provide) before you place the order. If you get a VOL or BTCOM ten digit number back and not a DFQ or similar short number then you've not got the right one. You should get two numbers. Much more detail about this on the thinkbroadband migration pages. Hopefully this will help someone else, information valid in late 2010.