its the 4 generation iphone

iphone 2g was the first
iphone 3g was the 2nd
then iphone 3gs was the 3rd.
the next one wil lbe the 4th installment in the series but the name iphone 4g isnt what has been actually stated it will be called. people are using that name to describe. if u want it to have 4g then you will have to wait till when att rolls out theier 4g network which they state wone be till about 21011(maybe) and by then some other carriers may have but that last part is opinion