Review: Seamless, Integrated Wi-Fi Calling on the iPhone 6

If you have poor cellular reception somewhere, you might want to make voice calls on your smartphone over Wi-Fi. The practice isn’t new, but it hasn’t been nearly as easy or seamless as making a standard cellular call.

You typically either needed a separate app, which can require the other party to have the same app, or a separate phone number that your contacts wouldn’t recognize. And even in the case where Wi-Fi calling was a built-in feature, a call begun on Wi-Fi usually simply dropped when you moved beyond Wi-Fi range.

Now, with the release of the iPhone 6, T-Mobile — the most aggressive promoter of Wi-Fi calling among major carriers — says it has solved those problems with what it calls the “next generation” of Wi-Fi calls.

If you have an iPhone 6 (or 6 Plus) on T-Mobile’s network, Wi-Fi calls can be made and received exactly like cellular calls. And they will seamlessly be handed off to the cellular network when you leave Wi-Fi range, and vice versa. Also, on the new iPhones, the company’s improved-quality “HD calling” will work on Wi-Fi calls, not just cellular ones.

T-Mobile calls this “Wi-Fi Unleashed,” and I’ve been testing it — at home, and at public Wi-Fi hotspots in coffee shops, airports and hotels in Maryland and Massachusetts. In my tests, it worked just as advertised. It simply required me to go into the iPhone’s settings and toggle a switch called “Allow Wi-Fi Calls” on the T-Mobile version of the new phone.

After that, my test T-Mobile iPhone 6 defaulted to placing all calls over Wi-Fi, if available, but with the same phone number the phone uses for cellular calls. These Wi-Fi calls could be made to any cellphone or landline phone, regardless of which network the other party was using.

The only indication that I was calling via Wi-Fi was a small change in the tiny service label at the upper left of the iPhone screen. It switched to saying “T-Mobile Wi-Fi,” even when there was no T-Mobile cellular service available.

There’s no special app to use, just Apple’s standard Phone and Messages features. And T-Mobile doesn’t charge extra for this service, or count Wi-Fi voice calls against your data usage. They do count against voice minutes, but the carrier notes that most of its current plans include unlimited voice minutes.

And T-Mobile says the built-in Wi-Fi calling capability works overseas, so you can avoid cellular roaming charges.

You don’t need any special T-Mobile router or Wi-Fi service, though the company is making available for free (with a $25 deposit) an advanced home Wi-Fi router called a “Personal CellSpot” that’s optimized for voice. (I didn’t test this device.)

T-Mobile says its system will switch to cellular from Wi-Fi if the Wi-Fi signal is too weak for quality voice calls.

In my tests, on my own home router and public routers, quality was the same as on a cellular call, and far better when I called another T-Mobile iPhone 6, because the company’s HD calling feature kicked in, even over Wi-Fi.

I was also able to conduct a standard SMS text conversation while on Wi-Fi with somebody who wasn’t using Apple’s Internet-based iMessage system.

Most importantly, I was repeatedly able to leave and reenter Wi-Fi range while talking or texting, without even a hiccup, whether the person on the other end was using T-Mobile or not.

For instance, I started calls in my home, and then went for walks, continuing the conversation over cellular, with no interruption.

Several times, in different places, I even put my test iPhone 6 from T-Mobile into Airplane Mode, killing its cellular capability, and then turned on Wi-Fi. Calls and texts still were made and received, with no problem. (This isn’t required.)

One new T-Mobile feature that I didn’t get to test is free Wi-Fi texting on airplanes using the Gogo Inflight Internet service.

The largest U.S. cellular carriers, AT&T and Verizon Wireless, don’t offer integrated Wi-Fi calling, though AT&T says it plans to do so next year, and Verizon says it will “in the future.” Sprint offers it on some phones, but without the handoff feature, and it isn’t available on the iPhone 6 from Sprint.

T-Mobile has offered Wi-Fi calling on scores of phone models for awhile, but says the iPhone 6 is the first phone it has sold that has the handoff capability. The carrier says that new software will bring this feature to some competing phones in the coming months.

If T-Mobile customers are running Apple’s new iOS 8 operating system, their iPhone 5s and 5c handsets can also default to Wi-Fi calling, but they lack the handoff capability.

I asked T-Mobile why it didn’t charge less for Wi-Fi calling than for cellular, and the company answered that the amount of Internet data it’s offloading for voice calls is too small to justify a price cut.

T-Mobile is so big on Wi-Fi calling because, although its network has been improving rapidly, it’s still small compared to Verizon’s and AT&T’s. If Wi-Fi calling becomes widespread, it would help narrow that gap. In fact, T-Mobile says, “Now every Wi-Fi connection works like a T-Mobile tower.”

The company tried this once before, about seven years ago. But back then, it cost extra, was limited and worked on only a few phones.

T-Mobile isn’t the only carrier offering default-to-Wi-Fi calling and seamless handoffs. A small outfit, Republic Wireless, does the same thing, and offers less-expensive plans. It worked fine when I reviewed it. But Republic’s service only works on Motorola phones, which are much less popular than the iPhone.

One downside involves 911 emergency calls. As with any Internet phone-calling service, emergency service operators can have a hard time tracking you down. So you have to register a default location — usually your home — when you first enable Wi-Fi calling on the iPhone 6. You can change this location later, and T-Mobile says it has ways of tracking you while you’re on the move, to help with emergencies. But it still isn’t as precise as on a landline phone.

So, does this even the playing field for T-Mobile against its bigger competitors with bigger networks — at least for iPhone 6 owners? That’s up to you. But if you’re running T-Mobile, or using T-Mobile, it sure helps.

This article originally appeared on Recode.net.