There are two ways you could keep your privacy online when asked for personal details. The easiest way - the way most people choose - is to lie. Give out fake details when they don't matter, especially to sites you don't trust. The harder way is to channel all your communications through an intermediary or broker. If you insist on privacy, then you need to trust someone else who will act as an anonymiser and firewall between you and the people you don't trust. You need this because once you give out your real details once, they are never secure again. Think of credit cards. If your number gets into the hands of the wrong people, you just need to cancel it, get a new one and give out the new number to the people you do still trust.
What you need, then are personal identity broker systems with unique disposable details. When you need to give out an email address to someone you need to trust temporarily, create a new one that automatically forwards to your real address. If they can't be trusted with that address, cancel it. Your main email address, and other fake addresses, remain unaffected, but anyone who got that forwarding address can't contact you any more. You can, in theory, do the same with phone numbers, and banking details too.
Mokalus of Borg
PS - Snail mail might work, but the service would be more complicated.
PPS - It would probably involve rented post office boxes.