Is it possible to use Signal or Telegram for crypto transactions? I heard CryptoCat messenger is for such needs, but interested in using those two mentioned above.
You can communicate transaction details to your counterparty using the app, but afaik neither of the messenger apps you mentioned have a cryptocurrency transfer system built into them.
So you'll need a wallet app, but otherwise you can communicate with your counterparty through the messenger app (agree on the amount to be transacted, send a payment address, etc)
For Telegram, there are bots that help do transactions and other crypto-related actions: https://news.bitcoin.com/six-of-the-best-telegram-cryptocurrency-bots/
However, I'd be cautious with these since not all bots are made by good people and I'd check up on them before trusting a bot with any transactional info.
For Signal, there are no options for now but the app's founder is very enthusiastic about crypto: https://bitcoinist.com/the-signal-founder-has-a-plan-to-fix-cryptocurrency/ https://techcrunch.com/2018/04/24/mobilecoin-moxie-marlinspike-binance-labs/
With enough time, they'll likely either to their own venture into the industry or add crypto transaction support in the app.