Sangoma sells some modules with a 1yr license (vs 25 year). Another example is Sangoma Connect. For these, you would need to purchase a license every year. I believe it still comes with support, so you would have perpetual support since the license and support cover the same period of time.
I’ve been all over this today for some renewals we need to do. A 1 year license gives you module updates and Sangoma support for the duration and it will stop working after that. 25 years gives you just 1 year of module updates and support, and it will work ‘as is’ beyond the first year. In essence, the module doesn’t need to receive updates after 1 year and bugs or incompatibility issues ‘should’ always be dealt with by core updates to the distro. There is also an intention by the developers to fix major security flaws as they arise. However, major updates to a distro release, such as jumping from v12 to v13, could break the module. Caution is therefore required when upgrading to a new FPBX version. I think the best approach to take is that 25 years means a year’s warranty, put simply, and then perhaps you’ll get a few years out of it for the money. They are all great value. Go with the annual license if it stacks up commercially, but 25 year licenses are more than appropriate in most cases. Happy to be corrected for any of this.