Generic access network systems allow specialized mobile phones to use their expensive mobile contracts on cheap WiFi networks. The benefit to users is that they can have phone service in areas where the mobile phone company hasn't seen it profitable to invest in infrastructure; the benefit to service providers is that customers will spend money on infrastructure themselves, and still pay the same rate as if they were using the mobile carrier's infrastructure.
A much more economical solution would be using a distinct VoIP service which tends to be on par with land lines or cheaper, and usually much cheaper than mobile service.
My mind is going. There is no question about it. I can feel it. I'm afraid. Good afternoon, gentlemen.