Snowden had some good comments here about Telegram in Iran: https://twitter.com/Snowden/status/947190333540061185
Telegram can only exist in Iran if it allows itself to be censored, basically. The alternative is for them to not exist at all in Iran.
The Iranian government cant force Twitter to do anything, but I assume they can shut down the Telegram app completely in Iran since they control the phone network and Internet there.
As long as the technical infrastructure for these apps are centralized, they are easy to shut down.