you have to download the facebook app from the play store (FREE)- I had MAJOR issues with this phone. I would be on FB (after tapping the icon 3-4 times to get it to open) replying to a msg or post and the keyboard would disappear and the screen would jump.
There is a Facebook app, does it all. It will work with both the Straight Talk data connection and WiFi.
NAV comes pre-installed but will update to Google Maps and that works fine. It can use your data connection and WiFi.
You can use Youtube via WiFi only. Straight Talk terms of service does not allow streaming content like videos and music.
Yes, if you can get the phone to work for that long. I had mine for a week and had to have it reset 3 times and it still would not work. Constantly froze up. Would not recommend this phone to anyone. I ended up buying an LG L40 Optimus Extreme through walmart.com. Excellent phone.
Yes it has YouTube, and GPS, but not Facebook. It is best to use the web browser for Facebook, as the Facebook app uses too much RAM and will exceed the phone's capabilities. It will run, but will shut everything else down. I just loaded a separate app for uploading pictures to FB and that works great.