Many of my friends already have the key fobs where all they have to do is have the key in their pocket or purse while standing next to the car, and if they push a button on the door handle, it automatically unlocks. Many manufacturers already offer this, and I'm sure many will follow suit. It's very convenient, as you don't have to actually take your keys out of your pocket.

I'm not sure how easy it will be to integrate the transponder into people's cell phones though. I bought my car four years ago, and I just bought a new cell phone a month ago. If I decide to buy a new car next year, will I have to ditch my iPhone and start using a "Toyota Phone" instead? (Will there be a "Corolla Phone," "Tundra Phone," and "Highlander Phone" also? Lol.)
Perhaps, each phone would have a replaceable card, like a SIM card is replaceable, and the auto manufacturer would give you a card with a specific serial number/code for your car, and you'd then place that into your phone.

I switch cell phones about every 6 months. Last thing I want is to be tied to a limited choice of phones just so I can have a smart key that I already have sitting in my pocket that I never have to take out.

Only in available in Japan, correct?

This might help:

http://hiwaay.net/~bzwilson/prius/key_fob.html

Also, search for "remote keyless entry" and "Atmel" or:

Remote Keyless Entry with the MAXQ3212 - Maxim

Bob Wilson