BHARAT SANCHAR NIGAM LTD. vs UNION OF INDIA .

The Supreme Court addressed the nature of mobile phone connections, determining whether they constitute a sale, a service, or both. It held that if the transaction is deemed a sale under Article 366(29A)(d) of the Constitution, states can levy sales tax; if it is a service, only the Central Government can impose service tax. The Court overruled previous High Court decisions, affirming that both sales tax and service tax can apply to mobile phone transactions, thereby clarifying the legislative competence of both state and central authorities in taxation matters.