Approx. 80 Kbit/s per parallel call are sufficient for using the cloud telephone system.

Depending on the codec, encryption or network quality used, the actual bandwidth required may vary slightly.
Allow for at least 20–30% additional bandwidth to compensate for fluctuations and parallel data transfers.
Example: For 10 simultaneous calls, at least 1 Mbit/s upload should be available.

With a VDSL connection with 10 Mbit/s in the upload, you can make up to 100 calls simultaneously.