I have a Uniden 508ghz expandable phone system with digital answering system that is 7 years old and I'd like to replace some of the handsets as sometimes they cut out during conversations and I can't hear the other person. They can usually hear me. But its like they hit their mute button. Obviously they did not. I've changed batteries recently and it did not help this issue. I need to know what handsets are compatible with this unit so I can replace them. The base and charging units work just fine. I'd only like to replace the handsets. [Uniden TRU8885 5.8 GHz Digital Expandable Cordless Phone with Answering System and Dual Keypads (Black/Silver)] Thank you for your assistance.