Google Fi will auto-switch between AT&T and T-Mobile but not Verizon, AFAIK.
Fi launched with Sprint and T-Mobile roaming and added US Cellular, but is presently T-Mobile only. I don't think AT&T has ever been a supporter carrier.
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Fi launched with Sprint and T-Mobile roaming and added US Cellular, but is presently T-Mobile only. I don't think AT&T has ever been a supporter carrier.