MUMBAI, India — In a narrow room filled with acrid fumes in one of the world’s largest slums, Chinak Ramtheol earns about $4 a day tending machines that melt and slice plastic trash into pellets for recycling.

He manages to save enough that he regularly can send a few hundred rupees to his family in rural Siddharthnagar, a thousand miles across India near Nepal.

“I have to go to a bank and fill out a form. That takes an hour,” Mr. Ramtheol said. “The bank is only open when I am supposed to be working, so I lose an hour’s pay.”

He’s intrigued by a new service that will enable him to send the money by cellphone to his family. MoneyOnMobile, an Indian start-up, is latching on to an idea that began six years ago in Kenya of transferring money with a few taps of the keypad on an everyday cellphone. That country’s mobile payment service, M-Pesa, has become so popular that most Kenyans these days send money, buy groceries and pay restaurant and medical bills and school tuition via cellphone — wirelessly transferring the equivalent of $21 billion annually. M-Pesa has inspired almost 200 similar efforts in other countries.