I'm not sure about FusionPBX, but FS PBX does have CharPMS integration. We just got certified by them. That gets you access to many hotel systems, including the one using HotelKey. They don't advertise it on their website, but they fully support it. We built a module to manage hotel rooms, housekeeping statuses, etc, using CharPMS API. Please reach out if you would like more details.
