Did you figure out what this is? I'm getting them, too. Caused me to go over. I tried to call it and it said "to the number you wish to dial followed by the # sign."
If you have a smart phone and have your unanswered calls forwarded to your Google Account. The 534-6641 number is what is used to transfer the missed call to a text. You can remove the feature by dialing *73 from your mobile device.