For another device like a smartphone to use any of the Bluetooth "services" which the micro:bit has, it must first be [paired with the micro:bit](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the micro:bit and exchange data relating to many of the micro:bit's features.
The Bluetooth IO pin service makes it possible for another device such as a smartphone to communicate with other electronic 'things' connected to a micro:bit's edge connector. You could for example, use your smartphone to switch on or off a light which is connected to the micro:bit or your smartphone could receive data collected from a sensor connected to the micro:bit. In fact you could do both of these things at the same time since the Bluetooth IO pin service lets you interact with multiple 'pins' on the edge conector in different ways all at the same time.
No additional code is needed on the micro:bit to use the Bluetooth IO pin service from another device.
For more advanced information on the micro:bit Bluetooth IO pin service including information on using a smartphone, see the [Lancaster University micro:bit runtime technical documentation](http://lancaster-university.github.io/microbit-docs/ble/iopin-service/)
