How many phones can you get with AirTalk?

I'm curious, could you please clarify for me the limitations of AirTalk when it comes to acquiring phones? Specifically, how many phones can one typically acquire through the AirTalk service? Is there a set number, or does it vary based on certain factors? Additionally, if there are any conditions or requirements that need to be met in order to be eligible for multiple phones, I would greatly appreciate if you could elaborate on those as well. Thank you in advance for your assistance.