Google Talk not working over Corporate Wifi. What can I do? Whenever I'm connected to our corporate wifi, google chat goes offline (i.e. the contact list fades to grey). 

I think this is due to a port setting. As far as I know only 80 (http), 443 (ssl) and ftp (21) are allowed from inside my company.

The problem is, that my android device automatically turns off the 3g connection as soon as wifi is available. 

I tried to find a setting for the Access Point, but couldn't find one. Likewise, I don't know if there is any setting in Google chat.

Android 2.2, LG-P500, Firmware V10-OCT-01-2010, Kernel 2.6.32.9

Do you have any suggestions?
The problem is, that my android device automatically turns off the 3g connection as soon as wifi is available.


Why don't you shut off Wi-Fi?

Since you can't control port forwarding or anything at work, there's not much else you can do.  Although, you could just ask and see whether they'd consider opening the Google Talk ports (443/5222/5223).