Germany's Call a Bike
points us towards Call a Bike, a (relatively new) service from Deutsche Bahn (the German railway company) that's available in Berlin, Frankfurt, and Munich. They leave bikes locked up around the city and when you want to rent one you just call the number affixed to the bike with your cellphone, enter your credit card number, and they give you a number that unlocks the bike. You can use the bike for as long as you like, at a cost of 6 cents per minute (euro cents, that is), up to a maximum of 15 euros per day. When you're done with it you just lock up the bike at the nearest major crossing and get another code that you call in with to confirm that you've finished with your rental.
