Sprint's Spark data network fizzles during voice calls

Sprint's new Spark service, a technical improvement to the 4G LTE service the carrier rolled out more than a year ago, promises its fastest wireless data connections speeds yet for smoother, faster streaming of high-definition videos and other large files, better Web browsing, and more. You'll need one of the newer, Spark-enabled Sprint phones to enjoy this benefit. Another Spark-phone bonus: support for HD Voice, a wideband audio technology that should improve voice quality—a weakness for many phones.

While we can't yet say for sure if such speedy connections are easy to find, or even possible, Consumer Reports engineers have confirmed that Spark can't do what older Sprint 4G used to be able to do: make or maintain cellular data connections during phone calls. That means no Web browsing, e-mail checking, Facebook or Twitter postings, or Map or GPS navigation assistance while you're on a call, unless you can access a Wi-Fi hot spot.

See how well Sprint Spark phones performed in our Ratings, plus check out our cell phone buying guide.

If you're using a data-dependent app when a call comes in, the app will stop functioning until the call is finished—not something you may want to happen while the GPS navigation app is guiding you through unfamiliar territory.

The funny thing is that most non-Spark 4G LTE phones you could buy from Sprint just a few months ago don't have this problem. For example, the original 4G LTE Samsung Galaxy S 4 has no problem juggling voice and 4G data connections. The Spark version of that same model, not so much. The exception was and still is Sprint's iPhones, which never had the ability to handle simultaneous voice and 4G LTE connections.

So, should you buy a Spark phone? That depends on whether multitasking while talking is important to you.

—Mike Gikas