There are many ways to share files between mobile devices such as drop box, GDrive and even BlueTooth. Those method will use email or device to pair up for sharing files. But I found there is an interesting way to pair up the devices. After I installed BUMP, as its name, a device bumps to other device, then two devices are paired. Finally, they can share files and contacts. I think it uses the GPS to track the location of device. If two devices have a same location, then they will be paired up, that is a very smart way to GPS. This app is available in Android and iPhone.