Great Potential, But Falls Short in many areas except for cost.
I have been a customer of BroadVoice for almost a dozen years. PhonePower acquired them during a period in which I was not a customer. I've now been a PhonePower customer for over a year. Here is what I conclude after a year of service:
1. They really are cheap (despite the "regulatory fees" that I believe they are actually required to charge).
2. They have cut corners on customer facing issues
3. Their website and apps are "stodgy".
On the cheap part... even after all the fees, PhonePower is a decent service for the price, decent assuming you have a good, reliable internet connection, and a tolerance for sluggish, powerless support. I have had a few outages, one caused by their provided ATA (telephone adapter) device. The support person was stuck in his script and v-e-r-y slow to respond in the chat session. Ultimately, I made more progress using Google searching (but then I'm network engineer).
Recently I wanted to switch my Virtual number and Primary numbers so the "calling number" displayed would be different when place calls, BUT... they won't let you do this over the phone, nor in their "Billing Chat" - even after they've gone through the trouble of asking you all about your account to verify you're the owner. Why the hassle, Phone Power?
Their website, and apps are underwhelming indeed, I find them rather user hostile. For example the Android app "softphone" continuously sends notifications about "connected", etc. Very annoying. The windows phone-power app by default automatically launches every time you log in, but there is no option in the app to change that behavior (you have to find preferences in the tray). The "Help" icon in the app does nothing.
From the apps and website you cannot change your voicemail message. Indeed, it seems you can only do this from a phone connected to the device.
I would probably STILL pick PhonePower over Comcast, definitely over AT&T. Vonage charges way too much for their service. However, do understand that if you choose PhonePower, you may find their tools and support frustrating.