A new report from CTIA shows that the amount of wireless data traffic handled by carriers continues its steep growth, up 120% from 2012.

CTIA’s annual survey of U.S. wireless operators showed that they handled 3.2 trillion megabytes of data in 2013. Meanwhile, companies including Cisco and Ericsson are predicting that by 2018, users will demand eight times as much data as was used in 2013.

Wireless operators invested about $101 per subscriber in capital expenditures during 2013 in order to handle the growth, CTIA noted, for a “record-breaking” $33.1 billion in capex spending. The per-subscriber figure excludes the cost of spectrum.

However, revenue increase rates continue to lag well behind the growth in usage. CTIA reported that wireless revenues went from $185 billion in 2012 to $189.2 billion in 2013.

U.S. mobile subscriber figures increased 13% from 2010 to 2013, to reach 336 million. Looking at that three year period, mobile data use was up 732%; MMS traffic increased 74%; and voice minutes grew by only 17%.

CTIA noted that the U.S. has only 5% of the world’s mobile users, but domestic wireless carriers invested 24% of global capex expenditures.

Other findings of the survey included:

• More than 10 billion MMS are sent monthly in the U.S., and more than 153 billion SMS.
• Monthly wireless data usage is at nearly 270 billion MB.
• Almost 40% of U.S. households are wireless-only.
• The industry now has more than 304,000 cell sites.