How can I use messengers for crypto transactions? 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)