A frequent question we encounter, particularly when replacing a damaged unit, is about handset compatibility. Opting for a new version of the same handset is generally the best choice, though not the only one. But what should you do if that model is no longer available? Firstly, not all handsets are interchangeable. The older 5-wire (4+n) analogue handsets were divided into two categories: AC call and Tone call. Any AC call handset could technically work with another AC call