To listen or to do a live broadcast will use the same amount of data per hour on your internet connection.
Every listener that is connected at say 48Kbps will use +/- 20 meg of data per hour from the server to them.
If you are broadcasting live, you also will use 20 meg per hour. (see below for accurate calculator)
Data Use to Listen or Broadcast Live:
48 Kbps =
64 Kbps =
96 Kbps =
128 Kbps =
192 Kbps =
320 Kbps =