I don't know which VOIP service you are looking at but I have an account with Skype and pay $38 every 3 months for world wide phone service. In the US, I have a cable modem with my broadband service from Comcast, and overseas I have ADsl service with a relatively slow modem. Even so, I can still make and receive calls with no problems, but sometimes the audio is bad when I'm overseas.
With skype, I have a local 510- area code phone number, which skype forwards to my computer if I'm logged on, or my cell phone overseas when I'm not logged on. The weak link in the chain is the local cell phone company where the audio gets garbled up and sometimes I can't make out what the is being said. When I want to call back to the US or to anywhere in the world, I would log onto my computer and make the call and the audio is fine on the other end.