Cannot get dial tone or any audio through handset associated with the base unit - though if in speaker mode - dial tone and conversations can be heard

My guess is that the handset somehow got de-registered with the base. You might try this procedure:

Attachment 46766


If for some reason it complains that the handset is already registered, you might forcibly de-register it first (then re-register)

Attachment 46767

Hope this helps,
WallyH