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A simple Android app can send and receive Ether to and from the Rinkeby Testnet. The code for all this can be found here. Using Web3j in Android is easy to set up and connect to the testnet using a node in the cloud. Creating a wallet so we can send Ether, loading the wallet and sending it back is easy. Sending Ether back is simple and easy to do with a simple app on an Android device with no need to be in sync with the network.