Ok.. Gtalk calls seems to work if i'm not using wlan. Don't know if it works from different wlan, because my pc where i make the calls uses the same network.

So Gtalk calls work if i use 3g, but i still can't make any Gtalk calls ,only answer. Button for calling is missing.

Okay, now I know that if i use Gtalk application on pc, then the button for calling appears to my n900. But if i use Gtalk with browser then button for calling is missing.