Fresh on the heels of a slew of new Google Phone rumors, the search giant has filed for a patent that would let users send mobile payments via SMS text message.

The patent, originally filed for in February but published to the U.S. patent office Web site on Aug. 30, describes a “Text Message Payment” system using a mobile phone that Google calls GPay. The application includes a detailed description of the would-be service as well as usage scenarios, such as consumers making on-the-spot text payments at a farmer’s market.

Google has already delivered a payment system for Web retailers dubbed Google Checkout.

While a GPay service could potentially be used by other phone-makers and service providers, it would seem to fit best as a revenue-producing element of Google’s own Gphone offering. Much of the speculation around Gphone has centered on ways that Google might enable free or low-cost calling by subsidizing voice service with things like advertising or, in this case, micro-payments.

Mobile payment technology isn’t exactly new, which raises questions regarding claims in the Google patent application. For instance, PayPal launched a mobile version of its popular payment services earlier this year.