Riddle me this: Vonage Soft Phone

I just looked into adding Vonage Softphone to my Vonage Account. It turns out that you cannot use Vonage Softphone with your existing Vonage Phone Number!

So I would need to add a Vonage Softphone line with a new number in order to use Vonage SoftPhone while I am away. Does that make any sense? shouldn’t you be able to have a SoftPhone that is the same number as your main Vonage line? so you can use it anywhere without having to lug your Vonage Router around?