I have a fine hairpin working thanks in large part to the great Mikrotik help pages. Using a pocket device having cellular data, and 4 internal wifi APs that are configured for roaming, one need not change anything to talk using a VoIP client when walking out of local WIFI coverage. But when our WISP went down yesterday all VoIP failed, as the static public IP was not available to the devices.

Any ideas how to fix it? We use a dynamic domain name to find the public IP.