Media for Any recommendations re: economy internet phone service- Vonage / Skype ?

I have heard of Vonage, Skype etc ? Which is most economical ?

We make between 6 and 12 hours of long distance calls per month.(mostly US)

What service/plan is best for us ?

Any companies to avoid ? Are all calls equally clear ? in terms of static ?

Also what headsets do to get. Would like to get a headset/phone that gives clear reception. Prefer to avoid the static on the line.

Any help would be highly appreciated.

Thanks Anna