After a long googling i found a solution using Pidgen on Linux/Windows, bypass/break firewall for gtalk/gmail chat, here it is:
configure your gmail account on Pidgen as follow:

Protocol: XMPP
username: your-gmail-username
domain: gmail.com
Resource: Home
Password: gmail-password
fill in Advanced tab as:

Force old port (5223)SSL: check/select
Allow plan text auth...: uncheck
Connect Port: 443
Connect Server: talk.google.com
File transfer proxy: leave default
Proxy type: use gnome proxy settings
Happy gmail chatting, behind firewall !
Cheers