The credit card is in decline. Here are a few hints of what might replace it. — D.R.

The New Ways to Pay

Twitpay

Type a friend’s Twitter handle, a dollar amount, and twitpay to transfer funds to their PayPal account.

Zong

Instead of entering credit card information anew for every online purchase, users fill in their phone number and the charge shows up on their monthly bill.

Square

The latest from Twitter cofounder Jack Dorsey, this 3/4-inch cube turns any iPhone into a credit card reader.

GetGiving

This mobile app uses PayPal to enable charities to accept small donations without the usual exorbitant credit card transaction fees.

Hub Culture

Travelers can avoid the hassle and fees of swapping dollars for euros by transacting in virtual currency in this international network of workstations.