Cloud has become a promising service model for mobile devices. Using cloud services, mobile devices can outsource its computationally intensive operations to the cloud, such as searching, data mining, and multimedia processing. In this service computing model, how to build an economic service provisioning scheme is critical for mobile cloud service providers. Particularly when the mobile cloud resource is restricted. In this paper, we present an economic mobile cloud computing model using Semi-Markov Decision Process for mobile cloud resource allocation. Our model takes the considerations the cloud computing capacity, the overall cloud system gain, and expenses of mobile users using cloud services. Based on the best of our knowledge, our presented model is the first to address the economic service provisioning for mobile cloud services. In the performance evaluation, we showed that the presented economic mobile cloud computing model can produce the optimal system gain with a given cloud service inter-domain transfer probability.