It seems Apple had to make certain sacrifices for this sleeker phone. One of them is the piece responsible for the vibration felt from a missed call or message. All the earlier iPhones, up to the iPhone 4, used the same motor assembly for vibration. The Next Web explains those phones used a rotational vibrator that worked by creating an imbalance of a counterweight.
Apple wasn't the only phone using this type of vibration motor. Most mobile phones use that same type. My daughter's cell phone vibrates so much that she doesn't even keep the volume on. Even with her phone across the room, we can all tell when she receives a new text or call.
The Verizon iPhone 4, however, introduced a different motor. Apple had switched to a more linear oscillating vibrator which led to a quieter, smoother vibration. It wasn't one that was going to be heard across the room. The iPhone 4S used the same quieter motor.
The iPhone 5 is now sounding noisier again with its vibration. If you haven't had a new iPhone since the initial iPhone 4, you most likely aren't noticing a difference, but if you have the Verizon iPhone 4 or the iPhone 4S, you're noticing it vibrating more loudly. This is because they have returned to the rotational vibrator.
The above graphic, courtesy of iFixit, shows just why Apple may have switched out the vibration motor. The smaller blue motor assembly is a earlier rotational one, where as the larger motor assembly is from the linear oscillating vibrator. The size is quite noticeable, and when Apple is promising a taller, more sleek phone, it had to obviously make some adjustments. It would definitely explain their switch back to the louder vibration sound.
In the larger scope of things, it's not a huge difference, but it helps explain that nagging feeling you've had since picking up the iPhone 5 that those muted calls and texts just sound louder coming in than they used to.
