Google’s Project Fi coverage map shows where data-only SIM cards will work

If you like the idea of the free data-only SIM cards now available through Google’s Project Fi mobile virtual network operator (MVNO) program, just know that you won’t be getting 4G LTE service everywhere.

Today Google published a coverage map for the data-only SIM cards, and it’s revealing. If you compare it with the coverage map for regular Project Fi SIM cards, you’ll see that these new cards rely on 2G or 3G service for a whole lot of places around the U.S.

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The 4G LTE service does show up in many cities and major thoroughfares, but once you go outside of those areas, things change.

In the New York and San Francisco metropolitan areas, the difference is not so big.

But if you zoom out on the map, you can observe the pattern.

And in some metro areas the difference is significant. Take Phoenix for example.

Same with Portland.

So before you go online and order one of these new data-only SIM cards by navigating to the Your Plan section of your Fi account page, just be aware of what you might be in for.