If you already have an S10, S10A, S11, T10, T20 complete system and just need to replace your headset, this is the item for you. This is the headset ONLY, no base included. Convertible headset includes over-the-ear hook as well as headband and ear cushion; features noise canceling microphone. Connects to base of unit with square, plastic, modular phone clip plug at the end of this headset's cord. (This headset does not feature QuickDisconnect.) Note: This headset will also work with the newer S12 complete system as an alternative replacement (without the in-use busy light).