If you are asking about for your business' personal use then it really varies. The line into our building needs to be upgraded so the voice quality varies and calls can drop which is very frustrating during a sales call or meeting.
We have a standard phone line as well due to this.
if you mean as a business then we have many VOIP customers and it seems the market is a bit saturated. There are some Latin American countries opeining up though so we will see.