The FCC has been publicly tangling with Verizon over data throttling lately, but the commission is reportedly also concerned about the practices of rival carriers.

"'All the kids do it' was never something that worked for me when I was growing up," FCC Chairman Tom Wheeler told Reuters last week.

For several years, Verizon has limited the data speeds of its heaviest 3G data users, but last month, the carrier said it would extend that policy to 4G LTE customers, beginning in October. Wheeler responded that he was "deeply troubled" by the move, and demanded answers about why Verizon was taking such steps.

Now, Wheeler is reportedly eyeing the policies of Verizon's wireless rivals. "My concern in this instance—and it's not just with Verizon, by the way, we've written to all the carriers—is that it (network management) is moving from a technology and engineering issue to the business issues," Wheeler told Reuters, "such as choosing between different subscribers based on your economic relationship with them."

An FCC spokeswoman confirmed to PCMag that the agency sent letters to AT&T, Sprint, and T-Mobile, asking questions about their network management practices.

A T-Mobile spokesman confirmed receipt of the letter, adding that "our network practices are consistent with the Commission's rules on the open Internet, are innovative and are good for consumers and competition."

"We look forward to reviewing FCC's letter and will respond as appropriate," Sprint said. "Sprint goes to great lengths to be transparent about its network management practices."

AT&T did not immediately respond to PCMag's request for comment.

Meanwhile, the FCC last week adopted rules that require SMS providers to support texting to 911 in an emergency. The big four carriers promised to implement text-to-911 tech by May 2014, and Friday's vote requires smaller carriers to do so by year's end. After that time, if a 911 call center requests text-to-911 support, text messaging providers will have six months to deploy it, the FCC said.

According to the FCC, more than 70 percent of cell phone users send or receive text messages, which are also widely used by folks who are deaf, hard of hearing, or have speech disabilities.