Banks' latest push: convincing consumers that shared taxi fares, split restaurant checks and other personal cash transactions are better handled via a smartphone than by handing over a few crisp bills.

A growing number of person-to-person (or P2P) money transfer apps for smartphones and tablets promise to quickly move money from your checking account to a friend's, or vice versa. There's no need to share account details with each other, the app designers say -- all you need is the friend's cellphone number or email address. And in at least some cases, it's free. Bank of America in late July became the latest bank to join the party, announcing that it was enhancing its apps to allow mobile transfers through a processing network called clearXchange, which is jointly-owned by Bank of America, Wells Fargo, and Chase. Wells Fargo launched apps using the same network in May, while Citibank, which has had an online transfer service called Popmoney since late 2010, introduced mobile transfers via its app in March. Chase, Visa, and American Express all have their own P2P transfer apps, as do PayPal and a number of other independent companies.

The targets are primarily customers in their 20s and early 30s, who are more comfortable using their phones for financial matters and who are just entering their peak purchasing years, says Dennis Moroney, a research director for Tower Group. "It's an opportunity to penetrate the household and solidify relationships," he says. Mobile commerce is swelling, and personal money transfers are expected to represent a large chunk of those transactions. By research firm Gartner's figures, worldwide there were $63 billion in person-to-person money transfers during 2011, accounting for nearly 60% of the $106 billion in worldwide mobile transactions. In 2016, such transfers could top $300 billion, says Sandy Shen, a research director at Gartner.

But U.S. transactions make up only a small fraction of that total, and experts say that banks' pitches here are still largely aspirational. "This is in its real infancy," says Moroney. Demand for mobile transfers is higher in developing countries because it's one of the more secure and efficient methods available, says Shen. U.S. consumers, meanwhile, are still dabbling in the mobile banking space. In June, 37% of consumers with Android devices used a banking or finance app, a figure that is relatively flat over the past six months, according to NPD Group. PayPal was the most accessed, with 11% using it, while other apps sat at the 5% mark or lower, says Linda Barrabee, a research director with NPD Group. Most of those who do use banking apps do so for time-sensitive actions, like making a last-minute bill payment or shifting money among their accounts to avoid an overdraft.

Consumers who want to give peer-to-peer transfers a try have plenty of options, and experts say which is best may depend largely on the kind of transfers you have in mind. Using your bank's app may require the least effort -- there's no need to share your account information, since they already have it, says Barrabee. Recipients of transfers may have it a little tougher: unless the sender's bank is also yours, or on the same processing network (as with clearXchange), you'll need to share your account information to sign up and claim the cash. And despite the pitch of fast exchanges, peer-to-peer transfers generally aren't as fast as making a trip to the ATM. Banks say mobile transfers can take up to three business days, with waits on the higher end of that estimate if the sender and recipient aren't using the same bank. Even writing a check may be faster -- some banks make funds from cashed checks available immediately, and others have apps that allow mobile check deposit.

Users should also pay attention to rules set by the service provider, says Shen. Banks often have limits for how much you can send in a single transfer, as well as each day. Citibank's Popmoney, for example, has per-transaction and per-day limits of $500 on "two-step transfers" -- those where the sender has only the recipient's email address and not his bank account number. There can also be fees. PayPal charges 30 cents per transfer paid with a debit or credit card, plus 2.9% of the transaction amount. (The sender gets to decide who pays the fee.)

A final caution: security matters. Banks say their networks are secure, and P2P transfer apps do require users to log in. Still, says Moroney, "It's always secure, until it's not." Consumers should take care to use strong passwords and take other steps to keep their phones secure.