This SpareOne cell Phone displayed at this CES claims to last for 15 years on a single AA battery.
It looks like your average cheap cellphone, except where the screen would sit is a transparent plastic void where a prominently branded battery sits instead. It's surprisingly solid and well put-together, opening the battery compartment reveals a sizable capacitor -- which is the real hero behind its purportedly long life. The two flashing LEDs indicate battery life and signal strength, but that's all the phone's gonna let you know. Call quality was basic and loud (like a phone from a decade ago), which sounds harsh to the ears. The only thing one can’t judge is its USP: the length of its battery life is something we'll have to address in a few year's time.
It'll be available at some point this quarter, will take any GSM SIM or microSIM (it has an adapter) and costs just $50.