Apple's solution doesn't offer true always-on, but rather it will enable your iOS device to always be listening as long as it is in a newly patented "smart dock". A couple days ago, Apple was granted a new patent titled "Smart dock for activating a voice recognition mode of a portable electronic device", which was originally filed in May 2012. As you can guess from the title, the patent would allow a smart dock to activate Siri on an iOS device.
The dock would have a clock and radio built in, and a microphone that would listen for an activation phrase, but all of the heavy lifting would be done by your iOS device. The smart dock would also allow for hardware add-ons like a removable hard drive, environmental sensors, a GPS module and more. Some add-ons, like the GPS could be removed and used separately.