Another warning. Most VOIP companies use ports 5060 through 5064 UDP for their technology and ARNET (DSL through phone company) blocks these ports. (Typical narrow minded Argentinos.) My temporary apartment had ARNET DSL (I have always had internet through cable company in prior apartments) and I could not get my VOIP to work (no matter what changes I made to the firewall on the router) on OUTGOING calls. Incoming worked fine. I had to sign up with SKYPE (as they use different ports) to make my outgoing calls.
So ... I continue to use Broadvoice (which is much cheaper than Vonage, especially if you are only making "in-state" calls for the number you obtain) for my incoming calls (thus everyone continues to call my same U.S. number) but had to sign up with Skype for outgoing. When I get permanent apartment (or my next temporary apartment) I will make sure they use cable (Fibertel, I think). I think there may even be a fiber-optic provider here (similar to ATT Uverse or Verizon FIOS) which is, of course, the mama-jama for internet and TV.