You have to add a custom repository to your Cydia installation (http://www.iphone3gsystem.fr/cydia/) before you search for H1Siri on Cydia.
We would recommend taking this as a proof of concept, instead of heading out and downloading it right now. Many, including our friends at iDownloadBlog, have had some difficulties actually getting Siri to function properly. It’s being suggested that H1Siri actually connects to Apple’s servers to get its information, which likely means that it’s only a matter of time until Apple puts the kibosh on the hack.
It’s also being reported by Grant Paul (Chpwn), that H1Siri is actually using copyrighted binaries from the iPhone 4S, making this hack particularly illegal.
There are a number of reasons why H1Siri is a bad idea, most notable is that all of your Siri requests are being diverted through a third party to get your responses. That means that someone, should you actually worry about this kind of thing, has access to all of your requests. We don’t recommend you do it, like, at all. Hell, the thing barely even works.
If anyone understands how annoying it is to have your phone rendered second-class by what seems like an arbitrary decision from Apple, it’s me. I remember jailbreaking my iPhone 3G just so I could get access to Qik and video recording features when the iPhone 3GS came out. It didn’t last long though. My jailbreak was a bigger headache than it was worth at the time. I’m going to be honest with all of you iPhone 4 users who want Siri: Siri is great, it really is, but it’s not worth the headache. It’s shiny, it’s new, and like everyone else, I couldn’t wait to get my hands on it. But, after using it for just over a month now, I can honestly say that I don’t use it nearly as much as I did in the beginning. I’m currently using it to set reminders and alarms, but that’s pretty much it at this point. I’m currently in Canada, so all of the location-based services are unavailable to me, so that might have something to do with it. But, in my opinion, getting access to a shiny new thing and potentially giving up your information to a third-party for Siri is not something that’s worth the risk.
Like we said, H1Siri as a proof of concept has shown that Siri on the iPhone 4 is a possibility and that there is very little standing in the way of an iPhone 4 port of the application, especially when it comes to hardware concerns. But, that’s pretty much it.