WAP Push messages - what and why are they?
I cannot answer all your questions, but I can tell you this, I was also getting a message regularly from WAP_PUSH_SI! with no content in it through my stock Samsung messages app. I would delete it and it would come back, even on airplane mode. So the problem and cause is from another app. That app is Google messenger. If you install a different sms app, then change the new app to your default sms app, then delete the google messenger app, you will never see this message again. I do not know why Google messenger is doing that, but I saw on a forum where someone has sent a complaint with a picture to Google regarding this issue. I know Wap_push_ is generally used to push some sort of promotion or advertising for paid products or services..it is all about money.