The method in which the data is sent to each other. Firechat uses Apple's proprietary platform Multipeer.
When we first developed Tin-Can, BLE was only supported on about 5% of android phones. For that reason, we decided to use Wi-Fi hotspots over Bluetooth. We didn't predict that the bloatware found on all android phones would make Tin-Can unusable on so many different devices. We had to set up rules for HTC phones and HTC phones on verizon and LG phones on Sprint and everything.
Because android is open source, every manufacturer AND cell service provided loads up each phone with apps and locks down certain features in whatever way they want. Developing for android using anything but the standard internet / communications features is an utter bitch, to say the least.
You can read more in this thread about the stuff: https://hubski.com/pub?id=142741