While carriers think of mobile data on their networks in terms of bits, subscribers think of it as useful or entertaining content. Finding the right way to charge for those services is hard, executives from Verizon Wireless and Nokia Siemens Networks said during a panel discussion at the Open Mobile Summit in San Francisco. It involves both ensuring the network can handle the traffic and making sure consumers think they're getting good value, they said.

"The simplicity of 5GB or 10GB, or whatever, may not be so simple to the users," said Hossein Moiin, CTO of Nokia Siemens. "The value of the content and the quantity of data that is consumed are entirely independent of each other today."

The real problem is network congestion, Moiin said. He suggested carriers might charge more for data consumption during busy hours and less when the network is lightly loaded.

The tiered mobile data plans that have sparked a heated debate over customer "bill shock" and the best way to allow new third-party services to flourish. The issues partly overlap with the debate over net neutrality, with . The U.S. Federal Communications Commission is on the issue.

The CTO of Verizon Wireless said his company hasn't found all the answers to those questions.