This depends on the hardware you use. Siemens Gigaset DEC Phones allow 2 concurrent calls, as well as Zyxel, Sagem and FRITZ!box hardware.
How many simultaneous calls can I make
This depends on the hardware you use. Siemens Gigaset DEC Phones allow 2 concurrent calls, as well as Zyxel, Sagem and FRITZ!box hardware.