Google's Project Fi comes to data-only devices, including Apple's iPad Air 2 & iPad mini 4

People who are already activated on Fi can order data-only SIMs for the service, up to a limit of nine per account. Aside from iPads, other officially supported devices include the Nexus 7, Nexus 9, and Galaxy Tab S. Unconfirmed accounts suggest that the SIMs may work with other products, like the iPad mini 2.

Tablets share in the same data pool as smartphones, with a fee of $10 per gigabyte, but to keep bandwidth under control Fi's data metering tools let subscribers see a per-device breakdown. Unlike phones, tethering is banned for data-only hardware.

Google is promising varying levels of coverage in over 120 countries, although people can still only sign up for the service in the U.S. via an invite system.

Until this week, Project Fi was restricted to a handful of Google smartphones including the Nexus 6, Nexus 6P, and Nexus 5X. The service's main advantage is that it costs just $20 per month before data fees, with unlimited voice and texting, and any data that goes unused results in a 1-cent credit per megabyte. A person paying for 2 gigabytes who only uses 1 gigabyte, for instance, will get $10 back.

The service preferentially connects to Wi-Fi, but when out of range connects to Sprint and T-Mobile's networks or else various 3G networks outside the U.S.