We will never be able to confirm 100% if these tests have been done or not, but the company has answered a question asked by Apple Insider about the matter and the answer has been that there are no plans to take Siri to other devices launched before the iPhone 4S :
Right now Siri is a key advantage for the new iPhone 4S, so keeping the exclusive assistant for this terminal is a logical move. However, jailbreakers have already shown that Siri can be operated without great difficulty on the iPhone 4, so perhaps in the future Apple will decide to extend this support. Not for nothing does Google consider Siri a major competitive threat in the search market, and Apple can use this ace in the hole .
Meanwhile, iPhone 4S sales continue to be strong with most Apple stores running out of stock. In Hong Kong, for example, iPhone 4S reservations from the web have sold out in ten minutes. It’s enough to distract you for a moment with your coffee while you make the reservation process.