Siri, the intelligent virtual assistant that's exclusive for the iPhone 4S, can now be installed in older Apple devices.

iOS 5 hackers Grant Paul and Ryan Petrich recently unveiled Spire, a new tool for installing Siri on previously unsupported models.

The tool is only available for jailbroken devices and will use about 100 MB of data.

Jailbreaking allows you to download apps and content outside the official Apple App Store or iTunes. While jailbreaking Apple devices is not illegal, Apple has announced that it may void the warranty of jailbroken devices.

Siri, a voice recognizing and talking assistant, has helped the iPhone 4S gain record sales despite the device's lack of design changes and 4G connection. Siri helps iPhone 4S users make calls, send text messages or e-mail, schedule meetings and reminders, make notes, search the Internet, find local businesses, get directions and more. Users can also get answers, find facts and even perform complex calculations just by asking.

Apple released iOS 5 as a free software update for iPhone 4 and iPhone 3GS in October. Siri was previously available in the Apple App Store for all iPhone models. But after announcing Siri is included with the iPhone 4S, Apple removed the existing Siri app.

Now Paul (aka Chpwn) and Petrich claim to have a solution that won't have copyright issues from Apple, although the tool may be more appropriate for tech-savvy Apple users.

To install Spire on your iPhone with iOS 5, follow these quick steps:

1. Jailbreak your iPhone. Various free-of-charge jailbreaking apps from the Dev-Team and others are available in the Internet.

2. Download Spire over Cydia. While installing, Spire will download Siri directly from Apple.

3. Enter your own proxy server address. Spire will only work if you have access to an iPhone 4S to get your authentication token. In other words, Siri won't be activated unless you can use a proxy server with iPhone 4S credentials. Hence, you need to spoof an iPhone 4S. Given that not all iPhone 4S owners are using Siri, you can negotiate with a friend or family member into renting out Siri on his/her phone.

"Spire is far from perfect, but at least at this point in time, it's the best that I can do," Chpwn said of the proxy issue. "Maybe in the future someone will find a way to evade the authorization requirement, but from my position here that's unlikely."