Hello Aspirant,
Three distinct engineers are involved in the design of mobile phones.
Electronic engineer -> Works on the design of electronics to be used inside the device
Computer engineer -> Works on the software to be used for the device and also works on the requirements of a consumer.
Mechanical engineer -> These design the housing and enclosures of the device.
You need to have a knowledge on Engineering Physics.

I prefer you to choose electronics department where you can have a very good opportunities.
Hope this will help you. Good luck.

Hello Mukesh
You can go for Computer Science engineering, Information Technology and Electrical and Electronics engineering because each of them deal with this subject.
You can also do some specialization course in that field in order to get an upper edge over others and that would surely help you.
Good luck