According to CNet, Apple's A5 processor includes noise-reduction circuitry licensed from a start-up called Audience. Audience's technology enhances speech and works well even when you hold the phone are arm's length ('far-field speech'). This explains the mysteriously larger A5 processor on the iPhone 4S and why the previous gen iPhone 4 didn't get the Siri via a simple iOS software upgrade.

The iPhone 4S has just a few advantages over the iPhone 4, including a an amazing 8-megapixel camera that captures HD video, a faster dual-core processor and of course Siri. However, if you don't care about the HD video or better quality photographs, you might be inclined to buy a new or even used iPhone 4 for less money or keep the iPhone 4 you already have. Many iPhone 4 users were none to happy with not getting Siri and assumed Apple was simply trying to force users to upgrade to the 4S. You would think Apple would have just come straight out and admitted there was a technical reasoning (Audience chip), as opposed to allowing their loyal customer base assume the "worst" of Apple. There are of course some hacks to get Siri working on the iPhone 4, but it'll never achieve the quality of the 4S.

I use Siri to dictate text messages and do some quick voice queries or even some math computations. Unfortunately, I cannot dictate an email using Siri. Siri-ously? Are you kidding me? Why can I dictate a text message but not an email. The lack of this feature annoys me to no end. Maybe a future firmware update will add this. Perhaps Apple wasn't ready to start having people dictate emails, especially when you consider the Siri server overloads they experienced.