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 Subscription/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 subscription/membership, AT&T LTE-M network connectivity and Live Tracking/Lost Dog Mode are not available.
- Why Does Fi Use AT&T's Network?
- What Is the Cost of a Fi GPS/LTE Subscription/Membership?
- How Do I Add a Fi GPS/LTE Subscription?