What's the cheapest Verizon plan?

I’m looking for an app for what people call VOIP calling—basically, I need some solid recommendations from the community for an application that offers the cheapest rates for calling the US

I'm on Vonage right now, used to use Google Voice too, but they seem pretty much the same here in the States,
so I went with the first one since it's cheaper for calling Canada.
I guess I'm happy with the service.

So, I was just attempting to set up an account over at Skype, but for some reason, it simply refuses to let me through. No matter what I try to put down for a username, I keep getting hit with this Sign-up Error (17)
message that says, "Please choose another username. This username already exists."
I’ve even tried using these ridiculously long strings of characters mixed with random numbers—stuff that shouldn't possibly be taken—yet it keeps flagging them.
Do you happen to have any idea what might be causing this?

Maybe the issue is just that the email address is already tied to an existing account.