WalletConnect is standard api widely used by Trustwallet, Binance, Kava, and other apps to connect mobile wallet with Dapps.
Most existing connect works with a minor modification: allow support for Harmony ChainId. (example Viperswap PR)

Adding Harmony chains

export const walletconnect = new WalletConnectConnector({
rpc: {
bridge: '',
qrcode: true,
supportedChainIds: [
ChainId.HARMONY_MAINNET, // harmony
ChainId.HARMONY_TESTNET // harmony testnet

Full dApp implementation

Follow the tutorials on for the respective platform.
For web, there is a reference implementation available at
Live demo:

Current supported mobile wallets