There's a sort of inescapable logic to what wireless network access providers will do if or when mobile VoIP applications are freely enabled, as some policy proponents advocate. Since the entire business model rests on voice revenues, the loss of those revenues will be compensated for in the form of higher mobile broadband access prices.
Existing best-effort plans might be the baseline. But new plans optimized for voice, or conferencing, or other applications, might well emerge. Of course, optimizing might violate some notions of "net neutrality," unless optimizing is available to any provider of voice over a mobile IP network, in which case it might not be a neutrality violation.
But those optimizing services will be an add-on.
You might argue providers can create replacement revenues some other way: selling content or advertising, for example. But the numbers don't work. Build your own spreadsheet and you'll figure that out. There is no conceivable new revenue stream that replaces voice revenues "one for one."
After some years of watching what happens in a robust, mandatory wholesale environment, even European regulators are starting to see what happens. Service providers start spending their money outside the home market, where financial returns are higher.
Investors aren't dumb. Businesses with low growth and margin prospects get less investment than competing alternatives promising a higher return. The current capital stringency is bad enough. Wait until you see a capital strike.