Since Petfon is positioned directly by GPS,it doesn't rely on cellular service or wifi signal. That means you don't need to use any internet during your tracking progress. It enables you to track your pets anywhere,even some very desert areas with totally no Wi-Fi or cellular signal. That means in theory, Petfon could be used anywhere in the world, as long as there is GPS signal with totally no additional fee.
However, there are still two other factors that may affect Petfon's positioning performance:
1, Using environment. If your living area is covered by forest or woods, it's not recommended to purchase Petfon
2,Google/Mapbox's coverage.  If your living area's map is not recorded by Google or Mapbox, it's not recommended to purchase Petfon.
3,Petfon doesn't work in some specific cellphone models. Including iPhone5s, iPhone SE and LG V20