Many emerging wireless applications are based on unique requirements such as edge data processing, distributed trust, and automation, which can be provided and enabled by blockchain technology through decentralization, transaction accountability, and smart contract-based automation. This article discusses opportunities and challenges of such blockchain-enabled wireless applications. First, blockchain technology and 5G system architecture are briefly reviewed. Then, an example wireless application use case is presented to illustrate the benefits that blockchain technology can bring to wireless applications. A set of pending research issues addressing some of the challenges faced by blockchain-enabled wireless applications is introduced. As a potential solution, a wireless blockchain middleware architecture (BlockWare) is proposed, based on a blockchain middleware layer connecting wireless applications and underlying blockchain infrastructure. The blockchain middleware layer interacts with various types of blockchain systems on behalf of different wireless applications. Thus, a wireless application does not need to implement complex blockchain functions, rather relying on the blockchain middleware layer and its services to leverage various underlying blockchain systems. This article also points out several research directions for future study, such as inter-blockchain interactions and interoperability, efficient blockchain transaction management, and blockchain-based messaging in future wireless systems such as 5G, beyond 5G, and 6G.