I'm using Skype as we have no landline in our flat. My pal's router (just) gives us free internet. Quality very good with two bars or more.
However, we're paying Skype - I think - £<5 month for free calls to landline numbers ONLY. About the same again to call cell phones. Feel I could do better with a do-anything program - though I protested loudly to T-Mobile and got a much improved deal - they were sucking money out of my PAYG deal despite using my American phone (with the 8 year old UK T-Mob chip in it.) It pays to be a squeaky wheel.
Because my life is split Across the Atlantic, I rely on Skype - talk to folk all around the world for hours a month. I wonder what will happen to that free lunch now MS are in the loop. I know I've said this before, but I'd sooner pay a cent a minute than see it decline into a low quality free for all.