I just received the Vonage Voice over IP phone yesterday. I simply plugged into my Cable Maodem router and immediately had a dial tone. I called my cell phone to make sure it works.
Turns out Vonag will even email you when people have tried to call that number. Voicemaill is included as well.
The quality was great, could not tell the difference between this and a "real" phone.
I can't wait to see how well it works from the DR etc. If it does work well, I will save between 400-600 per month on calling card bills!!
If it works from the DR, I see no reason it won't work from Colombia, Mexico, Brazil, Peru, Ecuador etc etc etc.