Citigroup Inc. has made the Obopay Inc. mobile payment service available to all of its U.S. checking customers.

As of Tuesday, all Citi checking customers were able to link their cell phones to their checking accounts.

In its original form, Obopay's service worked strictly from a separate prepaid account, but last year it began working with Citigroup to allow links directly into Citi accounts.

Obopay, of Redwood City, Calif., makes its service available through mobile Web browsers, a downloadable application, and text messaging. Senders pay 25 cents for transfers up to $50 and 1.5% of the transaction amount for higher values.

It also charges 2.5% for loading money from a credit or debit card, but it charges no fee for loading directly from a bank account.

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