VoIP calls don’t need anything special done to your firewall to make them work. This is because each side of the VoIP call is initiated from each side of the call.
The majority of firewalls will allow outbound traffic on any port (Lets call it a door from now on!) you wish. This is because the traffic is being initiated from within your network and the firewall knows you can be trusted.
Once it initiates traffic outbound on it’s chosen port to Yay.com it will keep that door open to Yay.com to continue to communicate with. It won’t be open to all, just to that conversation that your firewall and us are having at that time, whether that’s waiting for a phone call, receiving/making a phone call or the actual audio of that phone call.
In some very very rare cases, it it is of course possible that your firewall decides to close that door either midway through the conversation or right after it starts. It’s a highly un-usual scenario and if a firewall is configured this way, it will be limiting to not just VoIP calls, but many other things over your data connection.
In most cases, the simplest way to resolve a limitation like this is apply a wildcard to your firewalls “white list” that says allow all/traffic to and from anything @yay.com