M.G.
I have a friend with Vonage and when I talk to her the quality is not good a cell phone is better. Yes the one way speaker I have experienced, it is echoy and the volume is off - too loud on quietest on my 5.6ghz cordless where I have no problem when I speak with others.
Also, if you have/plan to get an alarm system there can be issues hooking it up (it needs a land line) and I am told that even if they can do it; there is still a delay.
Comcast Digital Voice usually runs about the same price special for the first year and then you call and ask for the retention department to get a decent deal after. Also, AT&T has the new stuff out & is offerring very good deals.