Am currently using VOIP with a Linksys PAP2 router. Upload speed 256. Quality is perfect!!!
VOIP was  designed as a military communications device within Israel... 
The company i have hooked into have commercialised that concept and is becoming rapidly popular due to its clarity and extra services.

An example of Extra services is SMS Callback, Web Callback and Mobile Callback.
SMS Callback- SMS a UK number with your accoun number and pword and phone number you wish to recieve the callback on and it will call the number you entered and tap into their FAIR pricing (not the lowest prices but very reasonable)
Web Callback- Log on to the website , enter your account details and enter a number to call you back on, the phone will ring then prompt you to emter your destination number.
Mobile Callback- Still limited to only Nokia 6100. but you can access their FAIR pricing from a mobile at local rates!!! this is the best one so far as you can avoid paying 49c per min from Mobile. Amazing service once it becomes available for more models 

Unfortunately Inbound numbers are only US toll-free, US, UK and others but no NZ or Aus numbers.

Very happy with the service so far and also the Linksys PAP2 as it turns any analog into a SIP Phone.