Mobile device payments

A system comprising:

• one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising:
• receiving, in a server computer, from a merchant computer an indication of a payment transaction by a user associated with a mobile phone number;
• providing a text message to a device associated with the mobile phone number requesting approval for the payment transaction, wherein the text message includes an approval code;
• receiving, in the server computer and after a particular amount of time, a message from the device associated with the mobile phone number;
• determining that the particular amount of time is less than a threshold amount of time;
• determining, in the server computer, that the message from the device associated with the mobile phone number includes the provided approval code;
• and
• based on determining that the particular amount of time is less than the threshold amount of time and on determining that the message from the device associated with the mobile phone number includes the provided approval code, obtaining account information associated with the mobile phone number, obtaining authorization for the payment transaction using the account information, and providing notification of authorization of the payment transaction to a merchant conducting the payment transaction.

A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising:

• receiving, in a server computer, from a merchant computer an indication of a payment transaction by a user associated with a mobile phone number;
• providing a text message to a device associated with the mobile phone number requesting approval for the payment transaction, wherein the text message includes an approval code;
• receiving, in the server computer and after a particular amount of time, a message from the device associated with the mobile phone number;
• determining that the particular amount of time is less than a threshold amount of time;
• determining, in the server computer, that the message from the device associated with the mobile phone number includes the provided approval code;
• and
• based on determining that the particular amount of time is less than the threshold amount of time and on determining that the message from the device associated with the mobile phone number includes the provided approval code, obtaining account information associated with the mobile phone number, obtaining authorization for the payment transaction using the account information, and providing notification of authorization of the payment transaction to a merchant conducting the payment transaction.