Your real question isn't how to make earbuds -- you could use off-the-shelf earbuds -- but how to build and program the appropriate bluetooth transceiver.
There's probably an off-the-shelf preprogrammed microcontroller and radio module which will do this. It may not be available in less than industrial quantities, though.
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There's probably an off-the-shelf preprogrammed microcontroller and radio module which will do this. It may not be available in less than industrial quantities, though.