How to identify whether the SMS sending company is qualified?

It's best to go to the operator's company to have a look. I'll believe that when I see it. If the company's scale is formal, it will be reflected in its business. If not, contact their personnel and have a chat. After all, it's up to you whether to make a voice group call or not.

As for whether your advertisement is formal or not, it depends on the content of the advertisement. If the advertising content is unhealthy, even if you do send it through mobile and China Unicom, it is illegal.