Vonage is a good alternative to landlines. Its a good VoIP service/provider. BUT there's lot of great alternative to Vonage.
VoIP has evolved a lot and its cheaper than ever. Quality improved too.
Now you don't have to get stuck with Vonage service if you think $20/month is not cheap. You can find better alternatives that will suit your needs, just make sure you search a lot first.
I don't have a landline anymore. I'm using VoIP service now and I average about $5 a month for my long distance calls including overseas calls.