Current we can make calls over Gmail to other Gmail and also do video calling but not from Gmail/gtalk to a cell phone.
But since Google has come up with this feature in U.S and Canada , hope in future we enjoy this in India in future.
Now you can tweet/blog from mobile via sms to your twitter/blog in India , making calls from gtalk to cell and vice versa phone seems not too far.
To learn more, visit Gmail.com/call. Calling in Gmail is currently only available to U.S. based Gmail users.
Advance Happy calling! for future.