There is no "best" company, it's all in what your needs add up to
Factors to consider when choosing the best VoIP provider:
* The history and reputation of the company. Is the company financially sound? Have they been in the internet phone business for a long time, or are they new at this? Are they on the "up and up", or are they entangled in lawsuits? The best VoIP providers are profitable, well managed, and highly experienced with the technology.
* The quality of support. Is the company committed to delivering the best possible service? Is their customer service and technical support staff always available, and quick to respond? The best VoIP providers will have 24X7 support and always respond to your issues very quickly.
* The quality of VoIP service. Is sound quality as good as a regular land line phone? Is the "uptime" of service 100% or near this? Does the VoIP provider offer call forwarding when your power goes out or internet connection goes down? Do they offer enhanced 911 (E911) service, which routes 911 calls to a local dispatch office and provides emergency operators with your location when calling? The best VoIP providers are always striving to provide top quality service, and are always proactive when it comes to delivering the latest technologies and service enhancements.
* What you get for your money. For most people, the main benefit of VoIP is getting unlimited local and long distance calling for a low, flat monthly fee. All internet phone service providers offer an "unlimited calling" plan, but the price usually varies from provider to provider. Vonage charges $24.99/month*, Opex costs $44.95 per month for unlimited home business service, Packet8 charges $19.99/month, FonVantage charges $29.95 to $39.95 per month for business-class service, Sunrocket charges around $16.50/month (with prepaid annual service), VoIP.com charges $16.58 a month (with prepaid annual service) and cable companies charge an average of $39.99/month for the same unlimited calling service.
* With the exception of Vonage, which recently included Western Europe in it's unlimited calling plan - most VoIP provider's unlimited calling plan typically includes only the U.S. and Canada.
* VoIP Service Features. Standard features like caller ID, call transfer, call waiting, call forwarding, call blocking, voicemail to email, voicemail, three-way conference calling, etc... are usually included with every VoIP provider's plan. The **** of feature and number of features varies with each provider, but most of the best VoIP providers give you every feature you would ever want for free. Unlike land line phone service (where you have to pay for these "extras"), features are usually free with the best VoIP providers.
Source
Voip providers 
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