Interesting to see how many patrons will be willing to download an app on their phone simply to correspond with a modeling agency.  I would guess far less than those willing to use the service otherwise.

I use telegram pretty often and it's a good, secure app. Much more preferred to just text.  
Frankly, I have had to block certain providers / agencies because they have sent unsolicited messages and they've come up at innpropriate times and can be accessed by anybody. Telegram is a good choice.