Sprint uses Carrier IQ's software on 26 million devices, and AT&T uses the technology on 900,000 phones.

The operators provided the information in letters sent Wednesday to Sen. Al Franken, who had asked the companies to provide details about their use of Carrier IQ's technology amid growing concerns over violations of subscribers' privacy.

The number of devices actively using the technology at a single time is significantly lower.

Sprint says it uses the software intermittently, and only 1.3 million devices may be tasked to collect and report data at any one time. For specific research requests, a smaller subset of about 30,000 devices is queried.

Of the nearly 1 million devices on AT&T's network loaded with the software, just 575,000 actually run the technology, the company said.

The Minnesota Democrat also received letters from Carrier IQ, Samsung and HTC. T-Mobile and Motorola, which were also asked to provide information on their use of Carrier IQ, have not yet submitted their responses.

AT&T and Sprint maintained that they only used the software to pinpoint problems with their service, such as dropped calls, sluggish websites and glitchy applications.

But to do that, the software does collect encrypted information about location. AT&T also uses Carrier IQ to collect telephone numbers sent and received by devices. The operator says it uses the data to determine why a particular call or text message is dropped. Sprint says it does not allow Carrier IQ to log telephone numbers.

Both operators said they were not using the technology to collect the contents of email, users' address books or online search queries. AT&T also said it did not gather information on specific website addresses, but Sprint said it already knows URLs through routing requests on its network.

Carrier IQ recently said it had found a glitch in its software that captured the content of SMS messages sent while a voice call was in progress. The resulting data was encoded and could not be read; Carrier IQ is working to fix the problem.

The operators’ explanations appeared to do little to assuage Franken's concerns.

"I'm still very troubled by what's going on," he said. "People have a fundamental right to control their private information. After reading the companies' responses, I'm still concerned that this right is not being respected."

Carrier IQ has been under pressure to explain how it uses information about wireless subscribers after reports emerged that accused the company of violating customer privacy. Carrier IQ says the data it collects is anonymous and only used to troubleshoot network problems.