As seen in a Slashdot comment:

I can confirm that talk.google.com is talking Jabber.

telnet talk.google.com 5222
Trying 64.233.167.125…
Connected to talk.l.google.com.
Escape character is ‘^]’.
< ?xml version="1.0" encoding="UTF-8" ?>
to="talk.google.com"
xmlns="j abber:client"
xmlns:stream="http://etherx.jabber. org/streams">

The last line of this is the standard response sent by a Jabber server prior to negotiating a login.

Here’s the /. article.