FT audio calls are in the same boat where if everyone you knows has an iPad you can make calls within that walled garden for free and don't need to be allocated a phone number. Admittedly more useful since so many people have an Apple product.
replyAnything where you want a phone number and to communicate with the rest of the phone network, I'd expect to pay money for it. Google Voice is the (only?) oddball here.
If you want to call POTS numbers, seems reasonable to pay a fee. voip.ms (of Canada, I think) charges ~ $2/month for a number and ~ $0.01 / minute for calls to US/Canada, calls to other subscribers are free. They work with deposits and a balance. Something in that range seems reasonable... maybe a little bit more if there's some work to make it specifically kid friendly (parental controls for incoming/outgoing calls?)
replyFair enough...$10/mo seems high. And I say this as someone in the target demo.
replyWhat price point would feel good to you?
replyI am working on a similar service for my own needs (and some other friends). But, my current plan is to hit $100/yr or so but the hardware is included in that cost. I am assuming $2/mo for costs of the number and minutes and retail costs for VOIP hotel phones is about $50. Hopefully the hardware costs amortize out and then I can offer a discount to users on subsequent years.
(If you want to go DIY you can save quite a bit of money too- I provided some breadcrumbs for doing that in my comment on the parent)