Prizm Institute conducts very good training in repairs of mobile phones and tablets. It provides more practical training than others as I have friends who share information about other training centers in Mumbai.
Right from basics they start the training from assembling and disassembling of phones and go upto advanced troubleshooting of faults. The trainers there are superb with excellent knowledge of the related subjects. They also provide job placement assistance to the passed out candidates.
The best part is they provide free technical support to everyone which is necessary for mobile phone repair technicians as they may get stuck if they get a phone with complicated faults.
I will recommend Prizm for its quality of training.