There are 2 methods to achieve what you want… one is to write a TS plugin based on Task Force Radio using webhooks and the other is to use a web based voip through html/java… the TFR style method is probably the better of the 2, but the html is probably the easier of the 2… Both are as best I can tell closely guarded scripts because of both their difficulty to make as well as their “prestige.”
I know that isn’t the answer you were looking for but sadly, I doubt you’ll see many public voip systems released