I tried to send a wav to my phone but was unable to play it.
After several tries, I fetched one of the provided files and found it was RIFF (little-endian) data, WAVE audio, IMA ADPCM, mono 16000 Hz while I had been sending RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 11025 Hz. Using the same format, it worked fine :) I also tried IMA ADPCM, mono 11025 Hz but it didn't work.
So, if you have the same phone, the magic command is
sox <input file> -i -r 16000 <output file>