Office Pbx If One Company Have Had IP PBX ,does It Work Through All Its Branches ,even If They Are In Different Country?

If one company have had IP PBX ,does it work through all its branches ,even if they are in different country? - office pbx

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IP-PBX can be implimeneted for all branches of the office on the same network and same ISP, or would be different if the offices are located in different countries and communities.