It's not illegal to not have Aadhaar. If one is willing to live underground, it's possible. You'll have to deal in cash (and maybe Bitcoin). A lot of people already do that. You won't be able to file taxes (A lot of people already evade, and won't be too hard without a bank acocunt). And let's not kid ourselves, there'll be plenty of SIM cards and phone numbers available on the black market. Or just get your friend or family to link. IIRC, there's no limitation of phone numbers per Aadhaar number. But yes, there are private individuals and companies that are exercising their inner fascist selves even if the government doesn't tell them. If your local chaiwala starts asking for Aadhaar, then you'll probably have to get one or leave the country.