Firstly, Telegram crypto wallet is not only available for premium users, contrary to what OP said. You can open and install it in your home menu through this channel https://t.me/wallet
Besides that there are 2 crypto wallets available on Telegram actually, and one of them TON Space is a real non-custodial one, you can fully access its mnemonic seed and import it in any other wallet supporting TON coins, you can also recover its access through email.
A custodial wallet is a service where the private keys (keys to access the wallet) are stored by the service. Examples of custodial wallets include centralized or private exchanges. This enables the service to offer unique features such as swaps, commission-free transfers, promotions, security settings, and more.
A non-custodial wallet grants users full control over their crypto assets, stored on their blockchain address. Only users have control over the private keys. Access to wallet and security control via Seed phrase are the main features of using non-custodial wallets. This provides users with bigger opportunities in ensuring the safety of their crypto assets, but also entails bigger responsibility.
With Wallet, you can easily purchase crypto by card, use the P2P Market and swap cryptos, such as TON, USDT and BTC.
TON Space gives you the opportunity to send and receive any Jettons and NFTs minted on TON, swap them and connect to decentralized applications (DApps).