How to use voice commands on iPhone 4?

I've tried to figure it out and have searched the Internet for a while. I know that if you hold the "home" button it brings up commands that can only control music and can call people. I want to know how to get more than that. Like with Siri or something. I have an iPhone 4 as listed in the title.

I don't believe Siri was introduced until the release of the iPhone 4S.

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