Hi.
You have to configure Port Forwarding on the Verizon FIOS Modem Router for iChat.
http://support.actiontec.com/doc_files/MI424WR_Rev._G_User_Manual_30.16.0_v1.pdf
Excerpt from pages 109 & 110:
"To set up basic port forwarding:
1. Click the arrow next to “IP Address forward to or select from menu” to display a menu and either enter the IP address of the item to port forward from, or choose an item from the drop-down menu (choose your machine by host name, since the internal ip address changes from time to time, after the lease time expires).
2. Click the arrow next to “Application to forward...” and select a pre-configured application from the drop-down menu (if iChat is not present in the list, you'll have to set up Advanced Port Forwarding).
3. Click Apply. The new port forwarding rule appears in the “Applied rules” table at the bottom of the screen. "
"To set up advanced port forwarding (custom ports):
1. Click the arrow next to “Application to forward...” and select Custom Ports from the drop-down menu.
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2. Enter the host name (from the drop-down list) or local IP address of the computer providing the service in the “Specify IP” text box. Note that only one local network computer can be assigned to provide a specific service or application.
3. Click Advanced.
4. Select the Internet protocol to be provided from the “Protocol” drop-down list. Depending on the protocol selected, additional options appear in the screen.
5. Select the connection with which this port forwarding rule will be active from the “WAN Connection Type” drop-down list.
6. To select a port to forward communications to (this is optional), select “Specify” from the “Forward to Port” drop-down list, then, in the text box that appears, enter the port number. If no port is identified, select “Same as
Incoming Port.”
7. If this port will be active all the time, select “Always” from the “Schedule” drop-down list. If the rule will only be active at certain times, select “User Defined” and click Add. Then, add a schedule rule (for more details about
schedule rules, see the “Advanced Settings” chapter of this manual).
8. If source and destination ports need to be specified, select Specify from the drop-down menu list (by clicking on the appropriate arrow), then entering the port numbers.
9. Click Apply to save the changes. The new port forwarding rule appears in the “Applied rules” table at the bottom of the screen."
Ports used by iChat
Good Luck.