[entropea]

>use a sim card bought with cash and never give out that number

This is near impossible now. I tried a few years ago to get an anonymous phone to activate an anonymous twitter account and you have to provide too much information to activate the sim card across the major providers and other companies that use their infrastructure.

[eythian]

It depends where you are. Some countries require ID, some don't. Last I bought one in New Zealand it didn't require anything, but I know Australia does.