For multi-dog households, you'll want to get one Fi collar + one GPS subscription per pup to track your pack.
Each Fi Collar operates as its own cellular device, so we would need to establish one AT&T line for each.
A subscription gives you access to the full capabilities of your dog's Fi collar - allowing Fi for remote access to your dog's location and activity. The cost of the subscription covers the GPS/LTE-M connection to your dog's Fi collar.