In a battle for relevance in the mobile payments space, mobile to mobile payment service Obopay has acquired social payment service Billmonk. Neither are disclosing the size of the acquisition, which is undoubtedly a tiny and probably stock for stock deal. The integration of the two services will first let users settle the debts they tracked on Billmonk instantly over Obopay’s mobile payment platform and eventually by email. You can see Obopay’s release here and Billmonk’s here. Founders Gaurav Oberoi and Chuck Groom will be moving to Obopay’s new Seattle office to focus on solving the “social accounting problem”.