How to Send Messages from React Native to IOTA Shimmer and Access Them in a Solidity Smart Contract?

The best way to achieve this concept on IOTA is by using the IOTA EVM Testnet rather than Shimmer, so I'll focus on the IOTA EVM Testnet for this solution.

To answer some of your questions:

Yes, it is possible to integrate a React Native application with the IOTA EVM Testnet. Since the IOTA EVM is Ethereum-compatible, you can use popular Ethereum libraries, such as ethers.js or web3.js, to interact with the IOTA EVM network from a React Native app.

Here are some URLs that might be helpful.

https://wiki.iota.org/isc/how-tos/deploy-a-smart-contract/ https://docs.ethers.org/v6/ https://web3js.readthedocs.io/en/v1.10.0/

Here is an example of a simple, smart contract that can be deployed on the IOTA EVM Testnet to send and receive messages.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

contract MessageContract {
    event MessageSent(address indexed from, string message);

    string public lastMessage;

    address public lastSender;

    function sendMessage(string memory _message) public {
        // Store the message and the sender
        lastMessage = _message;
        lastSender = msg.sender;

        // Emit the event to log the message sent
        emit MessageSent(msg.sender, _message);
    }

    function getLastMessage() public view returns (address, string memory) {
        return (lastSender, lastMessage);
    }
}

I suggest you deploy a smart contract in Solidity to the IOTA EVM Testnet. This contract will enable users to send, receive/get messages from the IOTA EVM Network. You can then create a React frontend and use Web3.js or ethers.js to interact with the smart contract.