In simple terms, if your circle A has 3G from Operator X, then you can use the sim card of X from circle A, anywhere in India, provided operator X has suitable roaming arrangements for 3G. This is not illegal. What is illegal is, a subscriber of Op Y not having a 3G license in Circle A, using Operator X's 3G in the same circle or any other circle.Further, Idea, airtel and VF can connect to one other network from the trio for 3G while roaming.