You do need to pass certification tests, but those are set by governments. Those tests may be defined with lots of input from industry and may be executed by institutes created by manufacturers as a group, but AFAIK, those institutes are so independent from the manufacturers that they won’t let commercial interests affect test results.
The issue with the original iPhone was that consumers were used to get a ‘free’ phone with their subscription. To do that, manufacturers need to work with a phone company.
The iPhone’s success was not a given and Steve Jobs had fairly stringent ideas about pricing. That made it hard to find a phone company to work with. IIRC, AT&T was a bit of an underdog in the market. That made them fall for Steve’s offer.