Calling an 800 number from the DR is usually much more expensive than calling a regular land line. Last I checked it was about 10 pesos per minute from my land line. If you have access to an internet connected PC and a mic/headset, you can download a program called SKYPE that will allow you to make 800 number calls for free. Now I don't worry about being on terminal hold while making such a call to those types of numbers. Two SKYPE computer users can call each other for free as well. The voice quality is better than normal phone lines.
SKYPE also has a service that lets you call the US (and many other counries) for about 2 US cents a minute. They use a different business model than Vonage does. Skype has you pay the equivalent of 10 Euros upfront and then you use it up as you call. No monthly fees are involved. I also looked into seeing if it was cheaper to use to call numbers here within the DR than using my local verizon land line, but it isn't.