Ok, but if Carmine Rosato hadn't said "Michael Corleone says Hello", it would have been confusing to the audience as to why Frankie gives evidence against Michael. Frankie knew the Rosato brothers, and knew they were backed by Roth, so he would most likely have assumed the hit on him was part of their ongoing dispute in New York. Sure Frankie would of been angry with Michael for refusing to kill the Rosato brothers after he asked him to at the Tahoe party, but Michael's refusal alone would not have been enough for an old-timer like Frankie to break omerta for. Frankie had to believe Michael was out to kill him, and I don't see how else he could have thought that without the "Michael Corleone says Hello" line.......

...there's people who would pay a lot of money for that information. But then your daughter would lose a father..instead of gaining a husband.