Use a lavalier microphone
Rodelav is one such example.
Use that with a phone.

1. Rode smartlav. Not Bluetooth. But why would you need Bluetooth? Most Bluetooth headset would probably suck at recording sound. Also, 2 people wearing Bluetooth headset in a pub doesnt seem normal.
2. connects to your phone which acts as a recording device.
3. Unless you're willing to spend a whole lot more on a better microphone + field mixer + recorder + boom stand + someone to hold it, this is the best option for you. It's also really really portable.
4. Paste lav mic behind clothes/collar. It will be discrete.
5. You may need 2 lav if you're recording 2 person.
6. Record sound on your main camera as well. This is to sync audio.
7. iMovie for basic usage and FCPX for professional use. For Windows, you can try Sony Vegas. If you prefer something more advanced you can try adobe premier pro or the industry standard, avid.

iPhone microphone by itself is not that much better than the camera.
However, you can use certain microphone on it like
http://www.zoom.co.jp/products/iq5

However... if you do so, might as well just get a mic for your camera directly.