Build word of mouth into the product: external network effects.
The marketing power of word of mouth cannot only be inserted into the “Promotion P”, but also the “Product P” as well. You can cleverly build word of mouth into the product’s development.
Anybody who uses Skype to call will recommend others to also install the Skype software. The more people you are able to Skype, the better.
Those who upload their jogging activities via Nike and iPod to the internet will also profit if lots of other people are also doing so – only by doing this does it enable “virtual battles“ to take place.
Panini sticker collectors profit when lots of their friends are also buying the stickers, as it allows them to trade with others.
All of these examples use “external network effects”: The products are more useful the more friends and family use them. We reckon it’s pretty clever.