I had no sound in TTS and none of the mentioned solutions worked so I gave up. Some time later I tried playing UT2004 and I had no sound there either. Wait a minute, both games run on unreal engine 2 and both have VoIP functions, we're on to something here...

I fiddled with lots of sounds and other options in windows and after some time I found the culprit:

I went to Control Panel > Sound > Communications and selected Do nothing instead of Mute all other sounds.

Lo and behold now I have sound. This method was tested and worked both in win 7 and win 10.

Hope it helps.