A:Answer Sanju - If you have the VTech CS6929 and CS6929-3 base connected to the same line, the cordless handset from one base will not communicate with the handset from another base. Both bases will work as a stand-alone phone. However, you can deregister the HS from one base and register it to another base so they would communicate with each other. You can also add the CS6909 accessory handset. The telephone base is expandable up to five handsets. Thank you! - VTech Support