This is a variation of Bill Me Later idea that brings phone companies and mobile authentication into the picture.  Payment by phone and authentication by phone are old ideas. Combine them with Bill Me Later along with 3D-Secure and you get: Bill My Phone.

Just like Bill Me Later, transaction starts by pressing the "Bill My Phone" button on a merchant's checkout page.  It uses 3D-Secure variation so the 3D-Secure merchant plugin redirects the customer to a 3D-Secure ACS at the customer's phone company using the customer's home phone number.  A soon-to-be-ubiquitous 3D-Secure authentication window with my phone company's logo pops up.  At this point, the customer can authenticate and approve the transaction using one of three way:

1. enter password into the popup
2. enter password into his or her cellular phone (WAP or J2ME)
3. answer home telephone and press some numbers displayed on the popup.

At this point, the transaction is complete and the purchase amount will be added to the customer's monthly bill.  Obviously, processors like First Data will need to get into the picture, but I think the chemistry is there just waiting to be mixed.