How about today? I believe that at some point, and it may be at a random time, the market app will check in to look for any updates to existing apps. It doesn't do this just entering the market app, and perhaps even when you install a new one.
So far today, the GTalkService is still
not running on my phone. I don't know if it will eventually restart or whether it's really "off". The only thing I've seen that definitely starts it, as expected, is to run the "Talk" program.
By the way, when I was doing my digging before in to what was causing the 3G traffic after ending a call, I spent some time examing the system log. I could see that after the call was terminated GTalk would begin an authentication process with a server. Not sure why it has to do that every time...
I'll ask again if someone else might have time to try these steps:
1. Enable 3G and wait for it to be idle (faint "D" is visible below 3G status bar icon)
2. Start up the dialer
3. Tap the first entry in the call history
4. Let the call be initiated
5. Tap End call
6. At this point the 3G "arrows" indicate data traffic. This usually happens 2 or 3 times and then goes back to being idle
Then, kill GTalkService from Running Services and try the steps again. For me, once GTalkService is gone I don't see any 3G activity at step 6. Thanks.