In exchange for allowing ads to run on your system, you may be able to receive a free operating system, OS upgrade, a new computer program or upgrade or even hardware could be free or heavily subsidized so long as you'll agree to view or listen to commercials.
So what kind of hardware are we talking about here? Well, Apple actually lists quite the range of possible candidates including portable and desktop computers, a network computer (NC), servers, electronics, iPods, game devices, mobile phones, wireless devices, email devices, personal digital assistants (Think iPod touch), embedded devices, televisions, set top boxes (Think Apple TV), etc.
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In other words, Apple is going to ensure advertisers that there'll be no way for users to get around playing their ads. In addition, Apple can further determine whether a user pays attention to the advertisement. The determination can include performing, while the advertisement is presented, an operation that urges the user to respond; and detecting whether the user responds to the performed operation. If the response is inappropriate or nonexistent, the system will go into lock down mode in some form or other until the user complies. In the case of an iPod, the sound could be disconnected rendering it useless until compliance is met. For the iPhone, no calls will be able to be made or received.