I've been using them since January. They're fine, decent voice quality, adequate customer service, much better than Vonage which I dumped in their favor. I've had occasional minor billing problems, all resolved quickly over the phone. I transferred my old number from Vonage with no trouble.
I use the $15 plan with 500 outbound minutes. It's kind of neat having a local calling area that stretches from Honolulu to Helsinki. They're a subsidiary of Primus, a Canadian telco that's been around forever.
I have a web page comparing various VoIP services at
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with signup links at the bottom.