You can have as many lines as you like all using just one number.
Let’s say you wanted 10 lines, BT could simply install 10 individual wall sockets and 10 phones but because these are then individual lines, when someone rings, the call will go to the first phone and the rest will remain silent. The second phone will only ring if the first one is busy, the third will only ring if both 1 and 2 are busy and so on and so on. So, imagine line 3 is ringing when line 1 finishes the call; because there’s no intelligence, it doesn’t automatically move the call and you need to go to phone 3 to answer the call. A phone system (PBX) provides a better way of queuing the calls and steering them to who ever is free to answer.
As for sending more calls down one line, this can be done either with digital lines (ISDN) which can carry two calls per line or by using internet based systems such as VOIP or SIP which can handle considerably more. With internet based systems, your lines are basically intercepted at the exchange and then routed over the internet to internet type phones at your office or in fact anywhere in the world. We use this method and it works well for us but you do need a good stable Internet connection and backups in place just in case.
Hope that helps.
Bill
