The self hosted AP makes sense, but could I pass SSID/passphrase if I were to take the RPi into someone else's home? I want to be able to plug the RPi into any random home and send SSID/passphrase to the RPi wirelessly. Then when the RPi receives the info it will connect to the Wifi network corresponding to the SSID/passphrase give. I would need to be able to repeat the procedure in anyone's home. I need my phone to "talk" to the RPi without the RPi being on any network connection. Is this possible?
It sounds to me like you're getting requirements mixed up with implementation.
Is it an actual requirement that you need the Pi to connect to an existing WiFi network? In that case you will have the problem of getting the SSID/passphrase onto the Pi.
Or is your requirement that you walk into someone's home, plug in the Pi, and can connect to it wirelessly? If that is your requirement, the configuring the Pi as an access point as several people have suggested will work, and any existing Wifi network in the vicinity is quite irrelevant.