Cons:

You absolutely cannot get 2FA authenticator codes from 90% of services. Many services that require a phone number even without 2FA just for "verify you're a human" or because they want your data or to verify region use shortcode services that also will not work with ANY VOIP provider.

You will not receive their codes. These companies vary from banking institutions to gaming companies to online shopping marketplaces and stores to a Google account (used to be you could get an automated phone call to verify an account, not anymore, must be able to receive SMS from shortcodes that are disabled for VOIP numbers to register and to recover an account) just about anyone you could end up doing business with.

A shockingly large amount of companies demand phone numbers and send verification texts before allowing you to do business with them, to create an account, to recover an account, to delete an account, to place an order, etc.

They really shouldn't, it's a bad security practice but companies love it because with a phone number they can lower support costs by just allowing people to do a self-service where they get an automated text and can unlock their locked account. They also love harvesting that data and preventing anonymization with VOIP numbers and the reduction of fraud and increase of reliable KYC that comes with requiring them.

And they all take it as a given that EVERYONE or at least 99% have a cell plan with a non-VOIP number that works with these and the 1% who don't they don't care about in the developed world and are an acceptable loss.

Still so much 2FA via SMS where I am in Aus.

I'd prefer to move everything over to something like Signal but I neeed a phone # to register for that but how do u tell the bank my Signal ID is @hanrhan.666

I've been trying to work this out since the beginning of the year. This is anecdotally what I've done, what works and what doesn't.

Most of my solution comes from JMP.chat for my phone number along with the cheogram app for functionality.

Basically I got a number for friends and family. I got a second number to give to businesses that don't care about VoIP (my dentist etc). ($5 ea). Cons here are that SMS groups are limited to 10 recipients. This doesn't work for my large family chats (I can get them but can't respond). Another thing I dislike is since its XMPP based, all contacts are listed as their phone number if in a group, so it's hard to tell who's in it. (Solo texts show as names just fine). They have a premium tier that routes differently to allow more than 10 in a group text, but I've tried that twice now and the actual phone calling gets screwed up. So I'm still trying to get it all sorted out (and I'm not optimistic) It's also a service only in USA and CAN.

My original number that I've had for 20 years and all big tech have assigned to me, I ported to google voice ($20 fee)

Since my original phone number was a carrier number it is already assigned to all the stringent companies like banks. They continue to use it without knowing its now a VoIP number. I have all SMS messages forwarded to my email so I don't have to log into google ever. It works perfectly for 2FA. Shortcoming of this is that any group texts the email just says you got a group text, but a single source text the actual text is forwarded. I don't use it for groups so its not a problem but just mentioning it as a potential con. Then of course, its legacy so opening new accounts won't work the same way since its a VoIP number now.

I bought a hotspot from calyx. By far the most expensive part of my solution. But it gives me WiFi access without a standard carrier (it does use T-Mobile but calyx doesn't track you like they do). Check them out to see if it fits your threat model. It works out to about $50/mo but the biggest issue is that its an annual lump sum.

Another option I've been trying is 4freedommobile. They have decent plans and are focused on privacy. Everything runs through their app for encryption. But I've found the app lacking both in UI and functionality. You can't do group SMS (which is apparently coming very soon) but my biggest issue is they require google play services for notifications. They state they don't, but they do. Hands down it just doesn't work without it. So that's a deal killer for me.

Honorable mention is the premium service Elfani. I haven't used it but have considered it. Its very expensive at $99 a month but is secure. However I don't see much on privacy so I'm not sure how different they really end up being from their base AT&T provider.

Why not is the question and that comes down to guessing. Sheep do what they are told so don't need to guess much there. Those who are not sheep have to go through a long journey to gradually keep increasing their privacy and unlearn the sheep habits we've been conditioned to have.

The end goal is to throw away your phone because you can do everything on your computer instead including buying a phone number, using voip and take and make calls. Phones are unnecessary spy devices used by sheep.

You can keep your cell number with jmp.chat. Call over wifi or data. They offer eSIM. View text messages on any device/program with XMPP support. 2FA works 100% like normal unlike VoIP. All data, calls, texts are routed through their VPN first, then the cell network. Any other inhouse XMPP chat not going to networks stay within XMPP. I have no affiliation with jmp.chat, I am satisfied with the service.

Pros is that you don't need a small, fragile device to use your primary communication method.

But the pros are that it's usually cheaper if you know what to look for.

The only time I call anyone is when my partner can't find her phone and I have to call it, because we set it so that my number is on the VIP list so it will ring even if it's on mute or Do not disturb mode.

SMS codes as mentioned and cellular data makes something with Sim card or e-sim a necessity. This can be mitigated by using a portable hotspot or cellular router/modem. Had a teltonika router that autoforwards the SMS as email.

If you care about security, don't put a Sim card in your phone.

Personally I don't have a VoIP plan. For archaic services that I can't live without and required a phone number, I use google voice or Skype. Its a vulnerability, so avoid if at all possible