What is Wi-fi Calling

Mobile Wi-Fi calling is a feature that allows users to make and receive phone calls over a Wi-Fi network instead of relying solely on a cellular network. Depending on your network it may be available when you have mobile connectivity, or only as a backup, if offered at all.

Why block it?

Wi-Fi calling is great, when it is great. But what if your local Wi-Fi is unreliable, or you expect to be interrupting it and want to block mobile Wi-Fi calling? Of course you could turn it off on your device, but I wanted to block it at the network level while I was dealing with some intermittent connectivity issues.

Carriers don’t seem to publish the IP ranges, but if you don’t mind blocking IPsec entirely, this article on optimizing your network for Wi-Fi Calling¹ has all the details you need:

Proto	Port Number	Description
UDP	500	Phase one
UDP	4500	IPsec encrypted packets

Alternative approach

Seamless Transition is well supported on the carriers and devices I use, which allows a user to leave Wi-Fi range and transition to the mobile network nearly seamlessly, although the reverse is not supported without disconnecting and re-dialing your call. But as a user you can take advantage of this, if you’re on a Wi-Fi call and suspect the network is causing problems you can turn Wi-Fi off and back on again to force the voice traffic over to the mobile network.

1. Is Your Network Optimized for Wi-Fi Calling? ↩