Fon LED flashesThe Fon LED flashes at constant intervals.LED indicates new messages in your mailboxThe flashing LED indicates that there are new voice messages in the mailbox made available by your internet telephony provider. Note:Since the mailbox is a service is made available by your internet telephony provider, refer to your provider for further information.
> https://en.avm.de/service/knowledge-base/dok/FRITZ-Box-6591-Cable/109_Fon-LED-flashes/