Our firewall was configured as per Google’s documentation to allow the Google Hangouts nee Talk client and the Android Google Hangouts app to connect. but to no avail.
With a little bit of troubleshooting I found that an additional port needed to be opened too. So here’s the firewall ports you need to open for Google Talk:
19302 – 19309 TCP and UDP
Additional Ports for various clients
<td> Clients </td>
5222, 5223, 5224
<td> XMPP clients </td>
5228 and 5229
<td> Android phones </td>
<td> XMPP federation </td>
This information was taken from Optimize your network for Hangouts
I hope that helps some of you out there.