How to apply for short message interface of China Unicom, China Mobile and China Telecom?

Talk to the operator directly. If you want to talk to all three companies, you can do it in large quantities. If you are small, the operator won't distract himself from talking to you at all. And it can only be a local interface, so you can't achieve triple play. It is more realistic to negotiate with the middleman, because you have mastered it.