If you’ve ever thought about ditching your existing wireless carrier, you now have a new option: Google.

The Mountain View, Calif. firm’s wireless service, Project Fi, is widely available for the first time as of March 7. Monday’s release follows an invite-only program launched last year.

Google’s Project Fi distinguishes itself from most other wireless providers in several ways. It’s powered by both T-Mobile and Sprint’s networks, so Project Fi phones hop between the two (as well as Wi-Fi networks) depending on which provides the best coverage in a given area. Customers using Google’s service get refunded for any unused data at the end of a billing cycle — so if you sign up for a 3GB plan but only use 2.5 GB, you’ll get the balance as a credit. And Fi users see no painful fees for using data services while abroad, although network speed is reduced.

I’ve been testing Project Fi using a Nexus 6P for about a week. Some of the service’s benefits, like potentially saving money on my monthly bill, would only reveal themselves over time. But others were immediately apparent: It was dead simple to sign up for the service, for instance. Google simply asked for my budget and found a plan to match.

Google charges $20 for “the basics,” which include unlimited domestic calls and texting, Wi-Fi tethering, unlimited international texting, and access to cell coverage abroad. After that, it’s another $10 per gigabyte of data. That meant my 3GB plan ended up costing $50 per month, which is either cheaper or comparable to similar packages from other carriers, like Verizon and AT&T.

Using Project Fi in my Queens, New York neighborhood resulted in generally fast speeds. But the numbers weren’t always consistent. One afternoon, I saw blazing fast download speeds of 32-38 megabits/second, based on results from Speedtest.net. Just two nights earlier, the figures were about half that. And in my downtown Manhattan office, speeds crawled to a dismal figure of less than one megabit/second. My Verizon phone showed the opposite results, with higher speeds in Manhattan and slower results in Queens. Your milage will vary depending on geography and other factors.

But Project Fi’s biggest downside is that it only works with a limited selection of phones. To use it, you’ll need a Nexus 5X, Nexus 6P or Nexus 6 — all Google-branded devices. Google hasn’t said if it will make more devices available on Fi.

All told, the prospect of a cheaper, simpler smartphone plan should be enough to get some consumers interested, at the very least. But Project Fi’s limited hardware selection will get many wireless shoppers to think twice before going Google.

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