Such devices like Xperia U,P.... iPhones, and some other devices which have no external storage but USB OTG supported, can use SD card or pen drive with OTG. There are many kind of OTG cables, but it is very hard to carry an OTG cable & a card reader all the time, so i am thinking of an OTG with card reader in a very small (as small as it can be) form which can be carried all the time.
the card reader will b stored(may be fixed) with the back cover(as shown in the pictures).
i am usuing very small card reader slot, thin wire(like insulated copper coil wire), a tiny siwtch(on/off).
As we know, in OTG pin 4 and 5 are shorted so i am usuing a tiny switch, when i switch on, the pin 4 & 5 are shorted & the cable will work as OTG, & when i switch off it will turn as a normal USB cable, so there will be no Battery Drain.
i am trying to configure it ,but having problem when soldering the wires with the micro usb male port.
The connections are so tiny, so it is very hard to make it alone, i tested it in a bit large form & it workes, but in small size as shown in figure it becomes very hard to make it ,,,,,,,
i am requesting you all to try it & make it by yourself,
if we can make it personally i think one day such cables will b available in market in very stable form for all usurs.