The DPH-50 is designed for one phone, not really all the phones in the house, but if you have it installed where you line box is, i suppose you could easily connect it to all the phones.
I don't believe this works quite as nicely as you would think with the DIR-655.
I could be wrong, but you still need one computer running with skype installed, that computer would also need the shareport utility.
Once the the DPH-50 was connected to the DIR-655, you can probably see the device using the shareport utility, before you connect to it, you would also need to install the DPH-50 software on the computer.
Pretty much, the DIR-655 would be acting as a usb hub for your computer for using the DPH-50. You would still need that computer to control the skype calls.
I could be wrong, as in my own place I use a wireless skype phone on my DIR-655, and do not have the setup you are checking out.