You can send information to any user that has your application installed. For free. This push comes as a pop-up message like an SMS, with the option for the user to open your application on a view specified within the push data.

Connecting to Apple's network means clearing a long task list and requires careful to maintenance to track Apple's changes. C4M provides you a simple push API to simplify the process so that you control the relationship with your users, without the hassle.