As mobile phone becomes popular in the society and many people can afford the cost, the demand of mobility is extended to teaching and learning purposes. One recent and significant change in learning environment is the demand of mobility. This paper will introduce a proposed framework of mobile learning. It consists of four functional levels: (1) mobile learning applications, (2) mobile user infrastructure, (3) mobile protocol and (4) mobile network infrastructure. The framework can simplify the design and development so that different parties (e.g. vendors, service providers, designers, developers) can address individual levels. A single party can build on the top of the functionalities provided by others. The functions of these four levels will be described with some examples. Moreover, practically knowledge management and learning community are two major issues in the mobile learning. In fact, they are the two states of changes in the learning paradigm, and will be discussed in the paper.