The rapid proliferation of mobile phones now provides an opportunity to harness their potential towards financial transactions. One form of such financial transactions is mobile payments. Our focus, in this paper, will be on certain design considerations for a mobile payment architecture. For widespread adoption, interoperability is a key concern. We first outline a previously proposed architecture, which supports interoperability. The design of this architecture requires the user to know only the beneficiary's mobile number in order to initiate a mobile payment. This is restrictive in the sense that only one bank account can be linked to a mobile number. To enhance flexibility it would be desirable, especially for merchants, to be able to link multiple bank accounts to a single phone number. We propose an alternate and enhanced design that allows the flexibility to link multiple bank accounts while also allowing the transactions to be conducted with just the mobile number. We evaluate and compare these two designs on various criteria. The details of implementation issues, advantages and limitations are presented. The analysis is a step towards the evaluation process of various design choices for mobile payment architectures. © 2011 IEEE.