Hi theston, I have used multiple Firefox OS devices in multiple countries - Brazil, USA, Peru, France, and Canada, and had no issues with data or voice reception in any of those countries (aside from carrier-related coverage issues). Is there any specific device you have in mind? It is always a good idea to verify that the device you are interested in supports the frequency ranges used by the carriers you plan to use. Please also remember that the Firefox OS devices are currently only GSM-based. Only networks with SIM-cards will work with Firefox OS (e.g. T-movile and AT&T in the USA). I hope this addresses your concern. Please let us know if you have any other questions about Firefox OS. - Ralph