The more things change, the more they stay the same. Apple’s newest iPhone finally brings 4G LTE to the device, a long awaited transition, but customers of Sprint and Verizon find themselves in a familiar situation. The iPhone 5 on both carriers will not allow simultaneous voice calls and data transmission, a feature AT&T long has lorded over its rivals. A combination of technology restraints and design decisions by Apple once again leave Sprint and Verizon customers without a feature that, theoretically, should be very simple.

Consumers want technology to work. They do not much care how. But a quick explanation of LTE, as simplified as possible, informs why the iPhone 5 on Sprint and Verizon does allow simultaneous voice and data usage.

On its most basic level, LTE is a wireless standard designed to send data from one point to another. It functions on an Internet Protocol-based standard that is more akin to Wi-Fi than traditional cellular service. LTE, for the most part, does not yet have a dedicated speech channel for voice calls, as “2G” and “3G” do. Companies are working on the function, known as Voice Over LTE, (VoLTE), but it is very limited and not ready for public consumption.

So how can many LTE phones, including Samsung LTE smartphones on Sprint and Verizon, support simultaneous voice and data? There are two reasons for this.

AT&T and T-Mobile operate on a standard called Global System for Mobile Communications (GSM). Sprint and Verizon’s networks are built on a different standard known as Code Division Multiple Access (CDMA). LTE is a natural extension of GSM. When smartphone manufacturers develop phones for various carriers, they decide what types of antennas to use based on the wavelength a carrier uses to transmit its signal, commonly referred to as a spectrum band. LTE runs on multiple bands, requiring multiple antennas. For AT&T, this is not a problem. The same architecture that supports its GSM-based voice function can also access data on LTE bands. For CDMA, a third antenna is necessary to handle this function. 

Consequently, when you make a call on your 4G LTE smartphone, your voice is not actually transmitted via LTE but rather a 3G network. The phone switches from the LTE band to the 3G band. On AT&T this requires two antennas. For Sprint and Verizon, it would require three to support the “switchback” to the CDMA-based 3G network. 

“This quite literally means you drop from 4G LTE to 3G WCDMA (where voice and data are already multiplexed) for the call, then hand back up to LTE when you're finished," wrote Brian Klug, senior editor of smartphones at AnandTech. "This is the way that voice works at the moment for all GSM/WCDMA carriers, and on all those handsets with LTE to date,” 

Samsung can support simultaneous voice and data on LTE smartphones because they decided to implement that third antenna. Apple did not. According to reports, the motivation for this was to not only create a very thin smartphone, but to simplify manufacturing so Apple can make as few unique versions of the iPhone as possible while still hitting as many LTE-capable markets as possible. As reported by Klug, according to FCC documents, two unique versions of the iPhone 5 exist that are nearly identical except for the types of antennas they include. To support simultaneous voice and data on Sprint and Verizon, Apple would have had to make a third unique version. Doing so would complicate the manufacturing process and cut into Apple’s profit margin, something the iPhone maker is very protective of.

In the end, the iPhone 5's functionality is motivated by profit. Sprint and Verizon customers are still going to buy the iPhone 5, with or without simultaneous voice and data. The are used to doing without it, so it does not behoove Apple to change its design to achieve a marginal result. Essentially, for Apple it is more headache than it is worth. 

The only way it will change, outside of a drastic change of course in Apple’s design and manufacturing approach, is when VoLTE becomes ready for public use, eliminating the need to fallback to 3G networks for voice capabilities. As it stands, VoLTE is not expected to be ready for widespread use until 2015-16.