I just want to present some of my recent work which can be useful for people trying to communicate their Arduinos with Android via USB.
First I released an Android library that can handle USB to serial converters GitHub - felHR85/UsbSerial: Usb serial controller for Android It is well tested and support the CP210x, FT232, PL2303, CDC interface and even the CH340/341 present in some of the cheap Arduino clones. It is open-source (MIT license) and it has been already used in some Arduino based projects like http://mouse4all.strikingly.com/. More information of how to use it correctly http://felhr85.net/2014/11/11/usbserial-a-serial-port-driver-library-for-android-v2-0/
Also I developed a Serial port terminal emulator with the library https://play.google.com/store/apps/details?id=com.felhr.droidterm&hl=es and a paid version of the same app without ads, different econdings and some VT100 emulation support https://play.google.com/store/apps/details?id=com.felhr.droidtermpro&hl=es