An easy way to check it to physically look at your modem, it must provide support for playback and recording of wave format audio. Technically, that means the device must provide TAPI "wave/in" and "wave/out" devices. In order for a voice modem to work with Windows TAPI, the modem must have voice drivers and sound devices.
Take a look at your modem... if it doesn't have these, then it probably isn't TAPI.
Don't quote me on this either. =P
