In the various tutorials for building an Android accessory that uses a USB connection, the first step is to "Select a hardware platform that can support USB host mode." Most of these tutorials claim that that means obtaining a device that is running > Android 3.1 (or one that is rooted, or a tablet, etc.). 

In my testing, it seems that, for a phone to support USB host mode, it not only has to be running > Android 3.1, but must also supply *power* over the USB cable. **Can anyone confirm or deny this?**

Most tablets seem to supply power over USB, but many phones do NOT. I can't find any place that will directly state that the phone must supply power over USB in order to be able to run an accessory as they all seem to loosely state that anything running >3.1 will work (as long as, at least, the device you're connecting to the phone supplies power). However, in all USB libraries that I've tested, I can make a connection to my USB device just fine from my tablet (which DOES supply power over USB), but I can't get any of them to work with my phone (which does NOT supply power over USB). Both are running > Android 3.1.

Note that I'm not trying to *power* my accessory over USB. My accessory has its own 5v power source and can even supply power over USB. I just want to build an app that will allow my phone to be able to connect to it, change it's settings, receive data, etc., but I can't get my phone to recognize if/when the device is connected. I don't know if that's because of my phone's unpowered USB, or if it's because of another problem with my phone and/or software. Unfortunately, I don't have another >3.1 phone to test with.

As a side note, the device I'm connecting to is an FTDI/Arduino board that I'm working on which, again, connects to the (powered) tablet just fine, but the (unpowered) phone claims that no USB devices are connected (even though the FTDI board supplies its own power).