what is the use of gmail ivitation.........

theyre using that one before...when theyre still under beta, but right now, theyre a;ready open to all members..which is good..but the chances of getting spammers is on high risk already

Actually you can only sign up for gmail without an invite if you use your phone to sign up. The purpose of the invite is they are still trying to make it a limited system since it is techinically in "beta" stage still for the past 3 years. I think the other reason for the invite section is because if someone sends you an email you can send them an invite if they aren't part of gmail already and if they do sign up for an account then their new email address is automatically added to your address book.

even i donnt know, but now a days spams r increasing

no use. spammers