Biggest example is with the iPhone. You cannot purchase one from AT&T to use on their network without subscribing to their iPhone data plan. If you only want to use it for voice and Wi-Fi, you are out of luck. They require this additional service charge. This is clearly not in the best interest of the consumer.
Likewise, if I wanted to get a phone and pay for data only, and use VoIP for the occasional phone call, I cannot normally do this, I still must pay for voice service.