On the Internet, volume of usage is different from magnitude of revenue. That is as true for Internet service providers as it is for application providers. On a price per megabyte consumed basis, mobile access is vastly more expensive than fixed access. That means revenue per bit is higher on mobile networks, compared to fixed networks.

But most consumption is skewed to the fixed networks.

Also, revenue-per-bit metrics tend to be non-linear as well. As bandwidth increases, the typical pattern is for cost per bit to decline, in either wholesale or retail markets.

For example, mobile average revenue per user (APRU) has declined in recent years across every region globally, by 8 percent a year, from $19 to $14 per month, with the biggest reductions in Africa, where ARPU declined 10 percent, and in Europe, where ARPU declined 7 percent a year.

Sales of additional subscriber information modules, lower-revenue M2M connections and retail price reductions all play a role in driving the lower ARPU trend. If those elements are separated, then ARPU for primary accounts dipped only about four percent a year.

Falling prices and rising disposable income, as well as pay-as-you-go plans, micro-top-up and low-cost handsets all have helped fuel adoption in emerging markets.

Still, in virtually every market, growing Internet access revenues will mean that a greater proportion of total Internet access revenues (not usage, necessarily) will skew towards mobile networks, and away from fixed networks.

In 2013, for example, consumer spending on Internet-connected smartphones, tablets and other devices will surpass home broadband service fees for the first time, according to PricewaterhouseCoopers (News - Alert).

Mobile Internet spending will top $54 billion in the U.S. market in 2013, compared with $49.6 billion in home Internet spending, the consulting firm estimates in the report, out today. In 2012, home Internet spending ($46.5 billion) slightly outpaced mobile ($44.5 billion).

In four years, nearly 286.7 million in the U.S., or 87 percent of the population, will have mobile Internet devices, while about 85 percent of homes will have broadband.

To be sure, usage is not the same thing as revenue. Most usage will continue to happen on the fixed networks.