Who is the best VoIP provider in the USA?

When we look for any service, we will gather the information about the product -- whether it gives value for the price, after-sales service and other customers' reviews about the product.

When we take all these into consideration, the best Voice over Internet Protocol (VoIP) in the USA is AT & T.  My sister and all my cousins are using it for a long time and they say, it is very reliable and service is also very good.