Hi, not sure where else to post this on the Fediverse, if there is a better community let me know and I will move this post there :)

I recently was trying to figure out an easy way to negate spam calls for my family. I am aware of tools like Spam Blocker however they are not fool proof. I don't really get spam calls myself, but the rest of my family does. The reason I suspect this is, is because I do not give out my phone number unless it is strictly necessary. I do not sign up for store memberships, when I'm on online shopping websites I usually just provide a dummy non-working number, and the only time I really do give my phone number out is in cases of emergency or for close family and friends.

This made me think, what if the family had a shared number to give out to take advantage of store memberships, online shopping, and whatever else. Then I could have everyone rotate their current numbers and do what I do where they only give out their main phone number in case of emergency. Being a self-hoster, this then evolved from a "family phone" that is kept at home, to "what if I could utilize SIP technology to let anyone in the family access the number from their own phones". I've tried looking into this on my own, but the most I can find is people with similar ideas abandoning the idea in favor of true telephony/SIP services.

The reason a telephony service won't work is a lot of the businesses have gotten smart about filtering phone numbers and will not let you sign up with one of these services (Especially if they have an old-fashioned 2FA method like SMS.) Not to mention, I prefer paying for my phone service in cash at a physical store for the added privacy of not having to give a real name.

What I was thinking was SMS USB Modem -> Home Lab -> SIP Program(?) -> SIP Clients (Phones).
Is this possible? Would SMS/MMS/Voice calls work? Is there a better solution that would be easier (While still working for my use case of using a real SIM card?)

Thanks in advance, hope you all are having a lovely day :)