#1 is when you talk directly to people who want to hear you.
#2 is taking #1 to scale by paying someone to carry your message for you, like advertising. Expensive, not always effective, but easy to scale.
#3 is when magazines and news outlets pick up your story because they think it matters. This is unpredictable but worth more because it comes off as unbiased.
#4 Is when, thanks to new technology and the democratization of distribution, people can pass your message to others, free, through blogs, Twitter and Facebook. Its costs little, very effective and scalable.
The tricky thing about #4 is that you can’t buy it like #2. And because it’s the most effective, companies try to make it work like #2, but it intrinsically doesn’t work like that, you can’t buy genuine desire to share. The only companies that are successful with #4 are the ones that make stuff worth talking about. If you really want to be successful in #4, don’t spend more money trying to turn it into #2, spend more money to change the product or service instead.