There are many payment gateway options available in India. Each one has differentiated offering. You will have to study the options in detail. Do negotiate on pricing, it's quite volatile.

1. To create mobile payments you should start with peer to peer payments and let people pay anyone from their contact list.
2. Piggyback on messaging apps for faster adoption.
3. You will have to figure out how people will send money into mobile wallet and how they can take it out from mobile wallet. This has to be done within the ambit of country regulations.
4. Once money is in wallet, let people send and receive money via your mobile wallet.
5. Create a new wallet for anyone who has not created a wallet but has received money
6. For mass adoption you will have to focus on interoperatibility, meaning:
6a. Ease of transacting between mobile wallets provided by different wallet operators (will potentially address all payment scenarios - peer to peer, customer to merchant, and business to business payments)
6b. Ease of transacting between mobile wallets and bank account (will ease cash-in and cash-out)
6c. Better dispute resolution processes
6d. Better fraud and risk mitigation policies