Occasionally, I have to reconnect my wife's Venu 4, 45mm, to her cellphone so she can answer phone calls with the watch. Although a conversation with the caller is not possible. Neither does she hear the caller nor does the caller hear her. After this call, the battery loses 1%/hour until she makes a soft reset with the watch.
By the way, it is also not possible to have a telephone conversation with my FR970. Callers and called people don't hear each other either.