Question: how to connect sony wireless wi c400 to iphone?
Answer: Unlock the screen of the iPhone if it is locked.
Turn on the headset. Press and hold the button for about 2 seconds. Make sure that the indicator (blue) flashes after you release the button. ... 
Display the devices paired with the iPhone. Select [Settings]. ... 
Touch [WI-C400]. You hear voice guidance “BLUETOOTH connected”.