Driver's side door won't open from the inside. Feels like there's a cable loose. Could use a blowup picture of the door.

well it sounds like you knocked a rod loose that connects
to the door latch. now you would have to take off door panel and fix this issue from the inside good luck.

Try replacing the unlock switch on door

either the rod that hooks to the inside door latch has broke at the fitting or the rod has simply worked its way loose.. remove door panel and you will find the issue

Try a slim jim first, down the side of the window. Or AAA or locksmith. If no luck, remove the seat first. Find the screws and bolts around the door handle and arm rest. Most Ford's have screws around the outer side of the panel. I don't believe your's does. The panel lifts or pops off. Once the panel is off, you can reach down and open the door. Just a note. I have done some to where the panel came out in pieces.

Get inside the backseat remove two screws that hold the side window. Gently pull the top plastic panel out all around and the panel will come out. It is held by about six clips. Then remove the screws and a nut off the bottom panel. These are all at the top of the bottom panel. Remove a couple of screws thatholds the inside doorl latch. Once all out then simply lift up on the bottom panel and it will come out. Remove the plastic sheet that overs the side door underneath the panel. Now you can see the whole mechanisim for the unlatch. On my truck the problem was with the top cable going into the latch mechanisim. The top cable came loose, out of the slot that held it in place. I pit it back into the slot and made a metal clip to keep it in place. If your interested I can add picture of the clip. Reassembled the door and was done in about three hours.

FIRST: try using the gas release lever from inside the car with the driver side door closed. My 2006 Jetta gas release lever would only work if the driver door were shut and I pulled the release from the inside car interior. Turns out it was a severed door wire (NOT THE RELEASE CABLE). Thus when the door was open, it stretched the damaged wire and so none of the door controls worked unless the door was closed. ie windows, trunk release, and gas release. It was a $600 repair at the dealership, parts and labor! :(

Cable may have come off a track wheel...may require replacement window regulator.

My friend just had this problem and he reached in and pulled the inside door handle back as far as it would go, and then let it go, allowing it to 'snap' back. For some reason this fixed it. We have no idea why. By doing this on one door, both rear door locks freed up and the rear locks are now working. Before, both rear locks were stuck and you could not open the doors from the inside nor the outside. Not sure why it works, but maybe it will work for you!

Either the interior door handle or the cable inside the door is broken. You'll need to remove the door panel and look to see what is damaged.

You will have to open it from the inside-Yes, I have done it and it takes about 15 min. or so.-I have also posted about 40 images, after I opened the door-In an effort to contribute a little to all the lost souls with the Curse of the F150 3rd Door issue. Hope this helps-BTW I just did this on 12/04/2011-found my particular issue-I will need a new cable, so I'll have to go to the dealer tomorrow and buy one. Also included images of the tools needed-Good Luck!
Link to the images are here>>>http://s289.photobucket.com/albums/ll220/techdispatch/F150%203rd%20door%20curse/?start=all