COD4: Escape Ambush, Escape Backlot, and Escape Crossfire

How to Get out of Ambush...

1. Get a buddy to go prone in that corner over there.
2. Start from the side and jump onto his head. This might take a few tries.
3. Start jumping as your buddy stands up.
4. Don't stop hitting jump and holding the forward until you are over the wall.

That's it enjoy!

To get out of Backlot...

1. Get a friend to jump onto the railing, then up onto the ledge.
2. As he crouches, jump from about 1/2 of the way up the railing onto his head. This will probably take a few tries, don't stop hitting jump or holding forward until you are up onto the next ledge.
3. Now, go prone and keep wiggling towards the right until you zoop through the invisible wall. This can get kind of frustrating, keep at it you will make it.
4. Stand up and carefully step forward until you are able to reenter the building on the left.

That's all there is to it, Enjoy!

Scraping the Sky in Crossfire...

1. Make sure you have RPG's and go up to the 2nd floor of that building.
2. Jump onto the peak of the chair, and then around of the corner of the wall snaking back onto the bricks shown.
3. Adjust your position until you can jump onto the pieces of sheet rock with the exposed re-bar.
4. Now, goto the top left corner of the rock and jump to make sure you aren't under the higher level. Equip the RPG's and aim the launcher at the small wall down on the ground level.
5. Fire, and as soon as you zoom in, jump upwards and hold back on the stick.

If all goes well you will be on top of the building, and be free to explore! Note that this glitch is very hard to do. Try not to get frustrated, although I really couldn't help it haha, Enjoy!