I know this is a really really old topic, and this is my first time posting here, but I thought I would share my solution to the problem with everyone.
I just got Verizon FIOS two days ago (15down/2up) and had a terrible echoing in my phones. It was obvious it had something to do with the cordless phone in my home because my corded one was ok. I decided not to rely on Verizon tech support based on this occurance and decided to test a theory of mine. I decided to unplug the router and see if the echoing continued. To my amazement, it stopped. Luckily for me I just switched from Comcast cable, which didn't provide routers, and decided to plug in my old reliable Netgear WGR614v5 and give it a go. Wow was I in for a shock. The interference didn't exist, coincidence, I think not. Well it turns out Verizon has no explanation for why a Netgear router would not cause the same echoing in my 5.8GHZ AT&T cordless phone, but for some reason it just works.
I hope anyone realizing this doesn't think that just because Verizon gives them a piece of crap, interference causing D-Link router that they have to stick with it at all. I talked to Verizon and there response was, "if it works great" and I asked them what to do with the other router and they said "do whatever you want with it, it is yours". So if anyone is having any problems, just go out and buy a Linksys or Netgear router and use a brand that actually works.
