Ther are a few ways in which you could do this, such as:
ACD Express
Ring Groups
Hunt Groups
I would say that the best option is ACD Express. But the easiest option to configure would be ring groups. The reason I say this is that yes Hunt Groups are really easy to set-up you do not get queuing, but with Ring Groups you do and there is no need to set-up any agents, just use your existing extensions.
You can either, point your DDI number to the new Ring Group, or delete your phone which has the DDI number on and then create the Ring Group with this number.
However, if you want to experiment with all three options, then I would just forward the calls.
I hope this helps