Most modern Android based devices support USB OTG function [1]. USB is a Host centric bus that means there is only one Host device and many different Devices can be connected to it. Using inexpensive USB-OTG cable it is possible to swich smarphone USB port from Device to Host, and connect external devices, if chipset and OS build allows this. Google provides detailed information on how to code USB Host [2] in your application.

[1] http://www.usb.org/developers/onthego/
[2] https://developer.android.com/guide/topics/connectivity/usb/host.html

I have just bought next inexpensive Xperia M5 phone with pretty nice hardware. However I already found those things to be missing or deliberately removed:

• USB OTG does not work (solved).
• CardBoard VR does not work.

Update regarding USB OTG – “it’s not a bug its a feature” – after you connect a USB device using OTG cable you need to run “Detect USB device” application that will make OTG work. Considering security this may be a good choice to allow external devices by hand.