Build a breathalizer into the mic section of a cell-phone, and have it measure the alcohol content of your breath as you start to speak, or breathe into it while waiting to be connected. If it detects mild levels of intoxication, it mutes the mic for a second and plays a pre-recorded message to the recipient of your call to the effect of:
“I’m sorry, but the caller you are talking to is inebriated. Please disregard anything they may say.”
If it detects extreme levels of intoxication, it disconnects you, dials a taxi firm, retrieves your location from a GPS component, relates it to a street via the Google Maps API, then text-to-speeches that info into a pre-recorded message to the effect of:
“I would like a taxi from [place name] to [home address]… yes, it’s [surname]”
So far four people have found the idea croissant-worthy, while two have inexplicably deigned to fishbone it. Weak.