After more than two years in beta testing, Venmo , a mobile payments service that lets people send money to their friends, is opening its doors to the public on Tuesday.

It is rare for a start-up company working in a highly competitive and crowded market like mobile payments to stay in test mode for so long, at the risk of having rivals overtake it. But the team behind Venmo, which first went online in August 2009, said it did not think the service was ready for mainstream use until now.

The service was originally designed to allow people to send small sums of money quickly via text message — $5 for a beer, for example, or $40 to split the cost of a meal. But eventually, the company released sleeker versions of the service as iPhone and Android applications.

The founders said this provided a much better experience for users. In addition, the company has shortened the time it takes to move money between the service and its users’ bank accounts. Previously it took several days to transfer money paid via Venmo into a bank account; now, that transaction happens overnight.

“We were waiting to perfect the payment experience before releasing it to the public,” said Iqram Magdon-Ismail, who founded Venmo along with Andrew Kortina. “We feel good about opening up now. We’re anticipating lots of volume and we have the right team in place to handle that.”

The service, which until now has been by invitation only, has also become adept at handling larger sums of money and more transactions during its beta phase. Venmo’s founders say the company is now processing around $10 million in payments monthly, a figure that grows by 30 percent each month. They expect that figure to total out at $250 million for the year.

The company does not charge a transaction fee to people using its service to send each other money. Eventually, as the company starts to talk to small businesses about using Venmo for payments, it plans to charge fees. Venmo also hopes to work with Square and other point-of-sale systems, in hopes of replacing the credit card altogether.

“The phone is the ultimate payment platform,” Mr. Magdon-Ismail said. “We want to keep payments among friends free.”

Backing from venture capitalists is helping to sustain the 23-person company for now, but Venmo declined to provide up-to-date details on who exactly those backers were.

Venmo also thinks it has an edge over companies like PayPal and Visa, which are also trying to roll out SMS- and app-based peer payment systems, because of its social component. The service hooks into Facebook and shows users a running tally of how much their friends have paid one another for different services.

“One of the reasons people prefer us and will prefer us in the future is just the fact that we are social,” Mr. Magdon-Ismail said. “You get more value out of sharing with friends.”