sort of makes sense
WiFi is becoming ubiquitous, and usually even where you have to pay for it, it's cheaper than mobile data*. At the same time VoIP is getting better, and it's already more worthwhile for me to buy a data package only with no sms or call minutes, use VoIP and internet-based messaging, and pay for calls / sms individually and as required.
I still see cell network being very relevant for mobile data (which will get cheaper as it's forced to compete more with WiFi) and 'guaranteed quality' and emergency calls. But smartphones SHOULD be optimised for WiFi
* excepting some hotels that charge extortionate rates, but nowadays in most places paid-for wifi is provided by third parties, often the phone operators themselves, at reasonable cost