Review: The Key to Wi-Fi Calling On T-Mobile's Uncarrier 7 Program

T-Mobile US (TMUS -0.08%) launched its seventh Uncarrier program last month. The first six installments focused on lowering and simplifying your monthly T-Mobile bill. This time, Magenta took a different angle and aimed to improve the calling experience.

Under the Wi-Fi Un-leashed moniker, T-Mobile says that all smartphones available today will support routing voice calls over Wi-Fi networks when available. T-Mobile is an old hand at Wi-Fi calling, having introduced the technology way back in 2007, but the company has never promised to support this feature for each and every handset before.

And if you own or buy an Apple (AAPL 0.52%) iPhone 6 or 6 Plus, the phone will even hand calls off between Wi-Fi access points and cell towers as you move around. Calls don't drop. This seamless experience is coming soon to other handsets, but Apple gets the early bird award this time.

Moreover, T-Mobile now offers a Wi-Fi router tuned for optimal Wi-Fi calling performance. The so-called CellSpot router is free to qualified T-Mobile customers with a refundable $25 deposit, or $99 for non-customers (or extra routers).

This is T-Mobile's tweaked version of the ASUS RT-AC68U model. The original version typically costs $200. Whether you're paying the $99 non-customer price or leasing one for free, this is a pretty great deal on the face of it.

I had to know more.

"We're making CellSpot available to customers so customers don't even have to worry about their Wi-Fi environment," a T-Mobile spokesman told me. "We view the CellSpot as an extension of our network, and the Wi-Fi environment is a key part of almost everybody's smartphone experience. We've been doing Wi-Fi calling for a while, and our biggest problem has not been the device -- it has been the Wi-Fi routers. People buy these cheapo things and get ready to upgrade in a couple of years, they're always out of date, all sorts of issues. So we really just wanted to make that problem go away."

OK. So I asked T-Mobile for a review unit, and I've been living with the CellSpot for more than a week now.

Here's what I found:

T-Mobile really didn't pull any punches with this hardware. The CellSpot, like its ASUS-branded sibling, is loaded with all you could ask from a modern Wi-Fi router:

• It supports the full gamut of popular Wi-Fi protocols, including the latest and greatest 802.11ac standard. With ASUS's original tweaks and multiple antennas, this network will be faster than the cable modem or fiber service you're connecting it to -- including gigabit services, with the right wireless device.
• It includes four gigabit ethernet ports for high-speed wired networking.
• It comes with two USB ports, including one high-speed USB 3.0 port. Good for attaching external storage directly to the network, or for plugging printers into the router.
• And of course, you get T-Mobile's own Wi-Fi calling tweaks.

T-Mobile US CEO John Legere, at an earlier Uncarrier presentation. Source: T-Mobile.

How does the router help T-Mobile users?

Now, most of these features are well within reach of any Wi-Fi networking professional or enthusiast. It's simple enough to find a high-quality router such as this ASUS mode, and then fiddle with the so-called quality-of-service rules until Wi-Fi calling works great under any circumstances. But that's not the target audience for this product. The vast majority of T-Mobile customers don't fit this bill.

If you found yourself glossing over any of the technical terms I've used here, T-Mobile is looking at you. Run through the setup procedure and start using high-quality Wi-Fi calling. End of story.

And it does work. The CellSpot connection never hiccuped or stuttered, even while playing several high-quality digital video streams on other wireless devices. T-Mobile's voice service tweaks work very well, and they take no take at all to set up. In fact, users can't even change them. Audio quality was good, or great when connecting to another HD Voice handset on T-Mobile's network.

The wireless range was longer than my regular (single-antenna) Wi-Fi router's, and I was able to walk several houses down the street before losing my Wi-Fi calling connection. I wasn't using an iPhone 6, so T-Mobile couldn't save me by handing the call over to a voice-over-LTE connection on a nearby cell tower.

What does T-Mobile get out of this crazy thing?
So T-Mobile is handing out very high-quality router hardware for free or for cheap. The company clearly sees Wi-Fi calling as a key strategy, worth shelling out some greenbacks to seed the consumer side of the market with higher-quality Wi-Fi routers. It's only fair to ask what's in it for T-Mobile.

T-Mobile is actually quite upfront about it:

• "This is like adding millions of towers to our network in a single day," said T-Mobile US CEO John Legere in the Uncarrier 7 press release.
• "It's like a T-Mobile tower in your home," said company spokeswoman Lindsay Morio when I reached out for more information.
• "We've effectively turned every global Wi-Fi connection into a T-Mobile tower," say the printed materials on Wi-Fi calling that shipped with my review router.

T-Mobile often performs poorly in network quality tests, hamstrung by a weak portfolio of wireless spectrum licenses. This may change in 2015 and beyond as the FCC auctions off some fresh spectrum batches, but until then, it behooves T-Mobile to find ways around the problem.

Wi-Fi calling does exactly that. Customers who connect via (decent quality) Wi-Fi can enjoy great call quality and no dropped calls, even if the cell signal shows a single bar or less. At the same time, these users don't connect to T-Mobile's actual towers, which have to divide up their resources between however many connections they're asked to handle. The fewer users you have fighting over the same bandwidth slice, the better their experience will be.

So Wi-Fi calling is a win-win for carriers with a low-end wireless infrastructure. That's why T-Mobile is pushing this feature as hard as it can, while spectrum-rich carriers  drag their feet.

And as a longtime T-Mobile customer myself, I'm putting down my deposit for my very own CellSpot as soon as I send back the review unit. At this price (free!), it's an irresistible way to get some 802.11ac action.