If you purchase any internal ADSL modem , you will have a(lead) with a small USA plug that goes into the modem and on the other end of the lead there is a standard BT plug. I have had this on all the modems I have owned since my first 2400bps one. If you purchased one today it will come with a BT line plug on the end. I find it stange that you have not come accross this before. External USB ones come with the small modem plug. Stange companys selling you a modem with a plug that will not fit into any filters they sell.