1. Ease of administration: obtaining, porting, and provisioning phone numbers, Caller Name, E911 settings, call routing options, etc are all very easy and quick to take care of from the website in real time with (usually) no additional communications needed
2. If it's needed, support is best in the industry (this reviewer has been evaluating and reselling VoIP products for 10 years)
3. Service does not go down
4. Support for a huge variety of IP platforms
5. Low cost! Review collected by and hosted on G2.com.