Siri is your personal assistant on the iPhone 4S and, despite the many natural commands you can use to interact, there are times you wish it knew some more. Developers have found a way to teach Siri custom commands.
According to those who managed this implementation, it doesn’t require a jailbreak solution but those looking to achieve this will have to “be on a network that lets you redirect Siri traffic through a proxy (via iptables, etc)”. Developer Aman Gupta said he was “redirecting traffic to Siri servers via a proxy that lets me return custom responses”. However, a jailbreak solution might be needed after all in order to teach Siri new things.