A service where you pay $5 per month, and in exchange, you get a temporary phone number to provide to websites and apps that require phone number verification. This helps cut down on spam, since many of these websites and apps resell your phone number immediately.

I don’t see why this would be illegal, since you still retain the identity of the subscriber.

There are lots of them: https://quackr.io/ https://receive-smss.com/ https://sms24.me/ https://temp-number.com/ https://onlinesim.io/

They exist. Services treat control of the number as equivalent to control of the account, and expect you to maintain that control.

Throwaway phone numbers are not a viable low cost or no cost alternative in most normal user signup scenarios, and they're implemented as a privacy invasive form of spam prevention for that exact reason.

I use google voice, and in the past other virtual phone numbers but many services don’t fully work. When you request a code, you never receive it and in some cases they tell you they don’t accept the virtual number.

The numbers would quickly be blacklisted by websites. You need a very large pool of numbers and make sure you don't reuse numbers too often. Not sure if it's practical.

In the US, you can approximate this with a cheap prepaid service like a Tracfone.

There are apps like Hushed where you can generate a working phone number for a pre-determined period of time.

I've always wondered what it would take to be my own telephone company and get an entire prefix, so I can give out unique phone numbers, kinda like how's privacy.com does for credit cards.