problem with removing the the dash idea is you will need to break the mount holding the screw on teh back of the deck/dash.
There are two tabs ont eh side of the radio, springs basically that just stick out and hold the radio aginst the back of the dash. Sometimes if the keys are not put in right it bends the tab/spring the worng way and then makes it impossible to get it out with out breaking the face of the stock radio off. Try inserting the keys while pushing the tips of the keys towards the ouside of the radio and as they said then push them all the way in. Now gently pry the keys out and pull, if it doesn't release then you need to find another way.
If you are not attached to the radio then just stick a small screwdriver into the same holes for the keys and pry the face off, it comes off easy and you can then see the springs and push them in. IF you do not want to break the radio then try dropping the glove box and going from the sides.