BT Synergy 700 answer machine cuts out?

I found 16 "messages" on my machine when I got home, but they were all just the dial tone. The reason, I found from one caller was that after the first few words of my recorded message the phone hung up and callers were diverted to 1571. My phone recorded the dial tone as the message! Is this a line fault or a problem with my Synergy?

Michael Fielding
March 2010