In India, in earlier days, each cellphone number will have a 'home area' generally conformed to the state you live in. If you are in the state where you bought the phone, you don't pay any incoming charges (voice/sms). Anyone else calling you will pay charges to connect to your number. If you are going out of your home state, you have to 'activate' roaming (it could be automatic if you wish to) and now you pay the 'roaming' charges from your home state to the current place where you are roaming.
Above is how it used to work when cell phones had just arrived. These days you pay a flat fee if you are calling another mobile from your mobile. Incoming call is free for the other party. Things do change if you call a landline phone from mobile (you pay higher rate because landline is mostly government owned in India).