As more consumers try out Fiserv Inc.'s person-to-person payment service, Popmoney, the tool is evolving to become as much a social tool as a payments one.

When users send or request funds, Fiserv presents them with a message field that allows far more flexibility than the short memo line of a check. Some consumers type a simple "Happy Birthday," whereas others provide detailed, itemized breakdowns to account for every penny being transmitted. It's no replacement for Facebook and Twitter, but it shows that users expect recipients to read and respond to their comments as though they were regular emails.

"The payment itself is the least important part of it," says Sanjeev Dheer, president of Fiserv's Popmoney division and the former CEO of CashEdge, which Fiserv bought last year. "Much more important is that the application facilitates that social interaction" illustrated in users' exchanges.

To be clear, Fiserv typically does not read these messages except as required by regulation, such as when other factors trigger a fraud or anti-money laundering alert that necessitates further scrutiny, Dheer says. Fiserv also used a short list of anonymized messages in a presentation to demonstrate Popmoney's use cases, though Dheer stressed this was a "one-time exercise."

Instead, as Fiserv fine-tunes its service it scrutinizes the more impersonal one-word categorizations users have the option to provide as they send or request funds. The categories include rent, childcare, entertainment and others. Fiserv also allows users to add new categories for their own use.

As more users send money to cover rent, for example, Fiserv can consider updating its payment system to make it easier to use for this purpose. For example, Fiserv could add an itemization feature to help a roommate collecting rent money to also request funds for other household expenses.

"We're adapting the application based on how we see people using it," he says. "As we advance the product, we may create specific variations of it that are adapted for those high-frequency uses."

Users can address Popmoney fund transfers to a recipient's email address or mobile phone number instead of needing to know a full account number. There are 1,400 banks that have signed on to use the service, Dheer says, and those banks have roughly 40 million online banking users altogether.

Some of Fiserv's clients, such as Citigroup and PNC Financial Services Group, are heavily promoting the Popmoney service, Dheer says. Citi promotes Popmoney through advertising, and PNC mentions the service prominently on its homepage.

As the Popmoney network grows, Fiserv also plans to take advantage of its Accel/Exchange debit network to provide faster payments. Currently, Popmoney allows users to send payments overnight or in three days.

But that's not good enough for some situations, Dheer says.

Through Accel, Fiserv can move funds in just 30 seconds, allowing users to almost instantaneously verify that they have received a transfer. Fiserv has not yet determined its pricing for its near-real-time service, Dheer says, though it expects its bank clients to charge a fee to their customers.

Fiserv plans to later expand this capability to other debit networks, Dheer says. Doing so would create much broader footprint for the near-instant transfers it would provide through Popmoney.

There are precedents for this sort of arrangement. For example, in 2010 the person-to-person payments provider Obopay Inc. sped up its mobile payments through a deal with First Data Corp.'s Star network.

Speed is important for Fiserv, especially as it faces competition from clearXchange, the person-to-person system formed by Wells Fargo, Bank of America and JPMorgan Chase, says Beth Robertson, director of payments research at Javelin Strategy & Research.

"Popmoney is really being challenged to maintain their prominent position in the market," she says.

The social component of sending and receiving money is vital, she says. It "puts everything in one communication channel, one interface for the consumer so the consumer doesn't have to go through multiple steps," she says.

Other companies place an even greater emphasis on the social aspects of payments, she says. For example, SmartyPig LLC (also known as Social Money Systems) allows users to publicize their savings goals and request funds on social networks instead of behind the login of an online banking site.