ummmm, I've got a Ford Fusion, and I could easily lock my key inside it. The car is a hatchback, and it has a button on the key remote that allows me to unlock the hatch lock. If I get out of the car, zap it with the lock button, then press the hatch unlock button, I can open the hatch without setting off the alarm, but the 4 doors are still locked. I put my key down inside the boot, shut the hatch, and hey presto, my key is locked inside the car. Easy.
Firstly, apart from being rather funny that you can actually manage to do such thing, I am assuming you have not got a master key as you wouldn't be in this current situation. If your not with RAC/AA ect then find somebody who you know that is willing to let you ring AA/RAC using there account acting like it is there car.