Google Fi SIM

Google Fi still markets and sells its own niche set of smartphones that are "designed for Fi," but has also opened its doors, officially, to any unlocked phone that wants to be on its network. For many, this is the final barrier to drop before trying out Google Fi, as it was quite a bit of extra hassle to change phones just to try out a new network for a little while.

But unfortunately, there are still barriers to be found further down the road. Unlocked phones on Google Fi don't get all of the same features as its own certified phones, and what you do get depends on the specific phone you bring. Let's break down the differences to help you decide whether bringing your own phone to Google Fi is worth it.

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Check device compatibility first

You need to know if your phone supports T-Mobile's network bands before you even consider going to Google Fi.

Before you get started with your transition to Google Fi, you need to know whether your phone will even work on the carrier. This one's pretty easy: if your phone is advertised as being compatible with T-Mobile, then it's compatible with Google Fi. Because Google Fi simply operates on the T-Mobile network, no further network bands or technology is required to use an unlocked phone on the carrier.

Google has a Fi network compatibility checker if you're unsure, but know that the compatibility checker isn't meant to be a complete list of all phones that are compatible — it's simply a subset of recent popular phones. But chances are if you're using a phone designed for the North American market launched in the past few years it's going to be compatible. That even includes most modern Verizon and Sprint phones, which still have the right GSM and LTE network bands for T-Mobile. Some international phones will work, too — just use Google's compatibility checker, or research the exact radio bands your phone has and compare them to T-Mobile's needs.

Best unlocked Android phones

Make sure your phone is unlocked

Once you've figured out that your phone is compatible with Google Fi, you need to check that it's SIM unlocked. If you purchased your phone from a carrier recently — or if you still owe money on a financing plan — there's a chance it isn't (yet) unlocked. You'll need to call the carrier (some have an online portal also) and request a SIM unlock code — sometimes that request will only be fulfilled if you've had the account open for several months and the phone is paid for in full.

If you already have your Google Fi SIM card, then you can simply put the SIM in your phone and you'll find out immediately whether it's unlocked — you either have service, or you don't. If you have a friend who has a different carrier than you and wants to swap SIMs to test, that will accomplish the same goal.

How do I know if my phone is unlocked?

You (probably) only get T-Mobile's network

Coverage may not be an issue for you, but do yourself a favor and check first.

Google Fi bills its service as providing more value because it operates on not one, but three, mobile networks at the same time: T-Mobile, Sprint and U.S. Cellular. That's true if you're using one of Fi's certified phones, but it isn't true when you bring your own device. Unlocked phones with a Google Fi SIM inside will only access T-Mobile's network, which means you need to know if that network is strong where you spend most of your time. Google Fi has a coverage map that lets you select whether you're looking at coverage for "designed for Fi" or "compatible with Fi" phones — to check unlocked phone coverage, choose the latter. In most areas, the difference isn't huge — but check your specific location and see whether there are weak areas using just T-Mobile.

The only caveat here, of course, is if you bring your own "Designed for Fi" phones to the carrier. Google maintains a list of supported phones that offer all of the advanced network switching capabilities offered by Google Fi, but the list isn't huge. It basically boils down to the North American versions of Nexus phones since the Nexus 6, North American Pixels, North American unlocked LG G7 and V35, and the North American Moto G6 and Moto X4. If you buy an unlocked version of any of those phones and bring it to Google Fi, you'll be able to use Google Fi to the fullest capability just as if you had bought the phone from Fi directly.

You can't use the Google VPN or automatic Wi-Fi switching

Another advantage of going with a "Designed for Fi" phone is to have access to its quick network switching between Wi-Fi and mobile data, facilitated by the Wi-Fi Assistant and Google VPN. Being able to quickly switch from mobile data to Wi-Fi networks while on the go was an important part of Google Fi when it launched, and has only improved with the addition of a VPN service that makes the transition completely seamless.

Unfortunately, none of that works on phones that aren't designed to work with Google Fi. If you bring an unlocked phone that isn't designed to work on Google Fi, then you miss out on the advanced Wi-Fi switching and VPN just like you miss out on the mobile network switching with Sprint and U.S. Cellular. Now this isn't the biggest issue, but it is one of the core features Google Fi does really well on its own phones and is something that can save you data and hassle throughout the day when you are within reach of open Wi-Fi networks. It isn't critical to the daily experience of using Google Fi like a regular carrier, though — it's just a nice-to-have feature that adds value to the service.

Wi-Fi calling and texting is a mixed bag

Beyond the main network compatibility aspect of bringing your own phone, the next thing to be aware of is compatibility with Wi-Fi calling and texting. This is something we take for granted when we buy a phone directly from a carrier, or when using a "Designed for Fi" phone on Google Fi, but it is in no way a given that your unlocked phone will have Wi-Fi calling and/or texting when you put a Google Fi SIM in it.

If you rely on Wi-Fi calling, you should consider a 'designed for Fi' phone instead.

Google's support pages list what you can expect in terms of Wi-Fi calling and texting for various models, but it's all pretty noncommittal — the phrase you see most often is "You might be able to make calls or text over WiFi." That's because there's an incredible amount of software variation between different versions of the same phone. Each carrier and region has different software on the phones that may or may not be compatible with what Google Fi is doing, and because Google can't manage that software remotely it can't guarantee the phone will work fully.

Your best shot for having a phone that will work with Wi-Fi calling and/or texting on Google Fi is to bring a North American-spec unlocked phone, or a phone that was sold by T-Mobile. Phones from international markets or sold by another carrier like Verizon or Sprint are less likely to have the right type of Wi-Fi calling software to support those features. In some cases, if you use Android Messages as your SMS app you'll be able to text over Wi-Fi, but not necessarily make calls.

Is this really a big deal? Well, if you live somewhere with weak T-Mobile coverage and therefore rely on Wi-Fi calling in your house this could be a deal-breaker. In that case, if you want to use Google Fi you'll need to pick a "Designed for Fi" phone that has full Wi-Fi calling and texting capabilities. Google Fi also offers better per-minute calling rates when roaming internationally and calling over Wi-Fi, which may be appealing to you — and something you miss out on if the phone you bring doesn't support it.

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