[cwojno]

Calling twice in rapid succession is an emergency feature for Android (possibly other) phones when in Do Not Distrub mode. It bypasses the DND when you call twice like that. Usually, only the numbers on your Starred list can call without getting blocked by DND.

The recipient may believe they had starred the number because of this, making them more likely to pick up the call.

[0xffff2]

On iOS you can choose whether to allow or block repeated calls, but as far as I can tell it's an all or nothing toggle. If it's enabled, anyone can get through by calling twice.