Push strategies work best for merchants that already have an established relationship with users. For example, cell phone providers proactively send (i.e. push) advertisements via text or MMS messages to mobile customers regarding promotions and upgrades. This permission-based marketing can be effective if personalized for the user based on personalized preferences, usage and buying behavior. However, push strategies are also effective for building demand for high-priced services (e.g., enterprise software) that are targeted to specific markets.