Is Free PBX free?

I'm curious about the cost structure of Free PBX. Could you clarify if the service is truly free, or are there any hidden fees or charges that users should be aware of? Additionally, if there are any limitations or restrictions associated with the free version, I'd appreciate it if you could elaborate on those as well. Ultimately, I'm trying to determine if Free PBX is a viable option for my business needs, and I'd like to have a clear understanding of the financial implications before making a decision.