It would be killer if Telegram could interoperate with at least 1 or 2 of the other services, which would allow it to ramp up adoption. Unfortunately Wechat is very insistent about not allowing 3rd-party applications to use their messaging protocol, and Facebook seems to have closed their XMPP interface as well. I would guess Whatsapp probably has the same attitude.
In this respect I really, really miss the days of Pidgin and those other similar applications which used to be able to put MSN/ICQ/AIM/QQ/Yahoo/Zephyr all on one interface. That seems impossible with the state of mobile apps now.