We use Microsofts "Office 365" for our email, wordprocessing etc.
We also use as part of it their "skype like" tool "Lync"
Lync can dial-out if given access to an "UM IP gateway (that) links UM to the physical IP gateway device or session border controller (SBC) so it can handle calls from your physical telephone system"
Do BT provide a "UM IP" gateway "in the cloud" and if so how woulod this interact with our existing physical numbers (delivered by three idsn lines to our nortel pbx)