How does one copy files from a computer to a 'smart'phone via bluetooth?

I want to transfer a file from my computer to a friend's 'smart'phone via bluetooth. I pair and connect but when I try to 'send' a file bluetoothctl tells me the target isn't acquired; when I try to acquire it nothing happens, neither an error nor a success report. Somehow his 'smart'phone manages to output sound to my computer's speakers, which aren't bluetooth but dumb, attached to the audio jack. select also does nothing.

We'll just use USB, but I'm interested in understanding the problem with Bluetooth.