Make multiple calls(tasks)

I have an telephony application, in which the server has 4 ports. That means the application can only take 4 calls at the same time. However I have many calls in the queue say 50, for example.

So my logic is take 4 from the queue, remaining 46. After the first 4 completes, take the next 4 from the remaining 46. Thus the remaining will be 42, keep going...

If one of call failed, it should be kicked back to the queue. Please check my logic..

string[] waitedCallNumbers = new string[50];
// get the numbers from somewhere
for (int i = 0; i < 4; i++)
{
    string dialNumber = waitedCallNumbers[i];
    TestRun(dialNumber);
    // not sure how to deal with queue--waitedCallNumbers after call 
}

 //This will start the threads that run the test calls
public async void TestRun(string dialNumber)
{
    await Task.Run(() => MakeCall(s_TelephonyServer,dialNumber));
}

private void MakeCall(TelephonyServer ts,string dialNumber)
{
   try
   {
       DialResult dr = Dial(dialNumber);
       // log result...
   }
   catch()
   finally
   {
      // dispose all resources
   }
}

Thanks.