Phone monopoly

We called Nana on Christmas Eve to wish her a Merry Christmas. Sierra had the phone and we told her to say "Merry Christmas" when Nana picked up the phone. She did, and launched into a conversation so we sat back and listened to see how long Sierra could maintain her end of the exchange without us having to intervene. We didn't say anything for the first 13 minutes, and then came on for a few seconds, but Sierra announced that she was not finished and demanded the phone back. We let her talk again and they ended up talking for about 22 minutes!