I was trying to give you the simple cheaper ways first.
Also I assumed that you also have a RG (Residential Gateway) that has voice communications also because that is what I have. If not things are easier.
When I talked about attaching a 2nd router to your device, I was thinking about myself having a couple of old routers lying around. Run a Ethernet cable from the "Sky" to another room and attach the 2nd (possibly cheaper and simpler) router.
Bear in mind that some routers have multiple signal sources at different frequencies. Some frequencies go through wall better. Actually one of my old routers is stronger than the newer 2Wire model I use, but it doesn't have VOIP and so would have to be piggy backed onto the 2Wire.
But anyway try simple, cheaper first.