I'm trying to use raspi 3 as ibeacon transmitter and receiver. I want to transmit and receive unique id,major id and minor id. However,it says I would need a bluetooth 4.0 usb for this. If raspi 3 has inbuilt bluetooth why would I require external modem for this?
The Pi 3 comes loaded with a Bluetooth 4.1 module. It should work fine.
I'm going to put my psychic hat on and presume that you're reading this tutorial on Adafruit. That looks to have been written to be as widely applicable as possible, and to sell large quantities of Adafruit's own USB Bluetooth module, which is heavily linked throughout. Because only the Pi 3 has built-in Bluetooth it's likely just easier to provide universal instructions that work on every Pi.