Thanks @leejorNot familiar with Fonality, but a quick search shows it to be a cloud based PBX service of sorts. That being that case, and you can establish SIP trunks to providers, which I assume you can, then, in theory, you could follow this guide...
https://www.3cx.com/docs/
and establish a SIP trunk to register to 3CX. After that is is a matter of constructing a dialling plan, both directions, that works for you.
Followed instructions, the Fonality phones shutdown.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.