Hi. 

I encourage your spirit.

See to make smartphone or tablets or any such electronic gadgets you must have a complete knowledge about how production works , what material is needed , what instruments and machinery is required , etc.

Well if you have completed your BE in electronics offcourse you'll be able to design and build hardware as well as software if you are good at programming .

I can suggest you start with small gadgets try to develop them at home and from that experience you can always have a vision to create wonders in your field.

Once you know how to tackle small small issue of the gadgets coming and working on them you master the skill and volla there you go 

 You have all what you needed .

Thanks for reading.

Good luck