It isn’t technically tough to do anymore, but you can only self-hosting the sip endpoint, you need to rely on and pay for upstream trunking.

Also, be aware that 911 or emergency service contact is all over the place. In Canada, VoIP providers do not provide 911 unless they have a pots tie-in somewhere, and there are still tragic issues where 911 calls are routed to dispatchers thousands of km away.

If you have any nontechnical people who expect all the features of a landline using this, don’t do it yourself.