A mobile authorization service may be implemented as a web-based service, hosted on an authorization service server, and may exchange messages with various computing devices of subscribers to the service, including mobile communication devices. The service may be implemented as a software application executing on the server, and may include a client portion executing on subscriber computer systems and/or mobile communication devices, or subscribers may interact with the service using a text messaging application or a web browsing application. The service may receive an authorization request from a subscriber and may send a request message to an approver. The approver may send a reply message to the service indicating an answer. After authenticating the reply, the service may provide a response to the requester. The service may store information regarding authorization requests and responses. An authorization service subscriber account may be configurable for an individual or corporate subscriber.