If you sign up for a Google App Engine account you will have the following statement in the Terms of Service:
"You agree not to use the XMPP API to operate or to enable any telecommunications service or in connection with any applications that allow users to place calls to or receive calls from any public switched telephone network."
Google basically is blocking any usage of XMPP to communicate with telephony networks. In practical terms is limiting any usage of XMPP API for a SIP/Jingle or H323/Jingle Gateway, etc...
Although it is not that bad, once it implicit allows the usage for Pure Internet Calling purposes. It remind me about the all discussion around FCC, on Google "fighting" with Apple to get his Application into IPhone AppStore.
As I mentioned before, all this overrated discussion is possibly part of a Marketing Plan to Advertise the Google Voice Service, as it showed itself a big failure so far.
Once Google is following exactly the same bounds of restrictions as Apple in the App Engine.
This post does not have as intention, judge the Apple or Google for their games and strategies. But it has the purpose of warning and public awareness about Voice Over IP Market, now played by new powerful players.