A Mashup is a Web page or application that combines resources or functionalities from two or more sources to create a new application or service. Combining the concept of Mashups with mobile devices can unveil a world of new Mashups, Mobile Mashups, satisfying the needs of niches based on the long tail theory and creating extraordinary business values. Given the potential of Mobile Mashups it is reasonable to expect a great number of them flourishing on the Internet. However, there are a number of challenges that might slow down Mobile Mashups going mainstream. This work sets the foundation on how to build Mobile Mashups. A reference framework has been developed in order to serve as a base for future work and help developers exploring Mobile Mashups. This reference framework categorizes Mobile Mashups by type and architecture, points out which are the best protocols and data formats to use in a mobile context, analyses different characteristics of Services providers and, finally, lists advantages and disadvantages of a Web interface for Mobile Mashups and raises a number of issues to take in consideration such as the page model and the different tools available.