If you're using an Android, get yourself an inexpensive USB-OTG cable. They're usually under £1. You can then plug in a keyboard & mouse (and anything else) to your Android phone.
If you have an MHL compatible device, you can also plug in an HDMI cable and use a bigger screen.
Something like http://amzn.to/1SgkguB will do the job. Of course, you might need to VNC into something to get the UI you want!
I have a unified OS across all my devices: Linux. Granted, I don't have a unified UI across all my devices…
I'd love to be able to plug my phone into a keyboard, mouse & monitor and have something like stumpwm available (i.e., something which actually takes advantage of having more than tap, three buttons, volume and power inputs).