No! The type of mobile carrier you use won't affect your use of the Fi Collar or the Fi App.
With an active Fi Membership, the Fi Collar will act as its own cellular device on the AT&T LTE-M network. Your smartphone can be on any cellular network - it does not need to be on AT&T for the Fi Collar to function.
Note: Without a membership, AT&T LTE-M network connectivity and Lost Dog Mode are not available.
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