How to let my voice modem play wave file

I try to use voice modem as waveout device
and use low-level wave API to play a wave file.

Details:
Use TAPI LineOpen() ,LineGetID() to get modem's ID
use this ID call waveOutGetDevCaps() to check support wave format
return WAVEOUTCAPS's dwformats == 32768,all PCM format is not support

use this ID call waveOutOpen() with all possible parameters is return error code 32(means not support format)

Anything wrong or It's impossible to let my voice modem play wave file

Someone suggests me use AT command set,but it seems complicate ,
Is this the only solution?

My modem is CommPack v.90 56K

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