ARE 3 PHASE PANEL WITH MAIN BREAKER ABLE TO OPERATE PROPERLY WITH 120/240V SINGLE PHASE SYSTEM. IT IS ASSUMED THAT THE ONLY TWO HOTS ARE ON TWO OF THE THREE TERMINALS. ARE THERE ANY CODE VIOLATIONS WITH THIS? IF SO WHAT ARE THE TECHNICAL CONCERNS IS THE CODE MITIGATING? IS IT JUST UL DIDN'T CERTIFY IN THAT CONFIGURATION?
Are you talking about connecting the neutral to one of the normally ungrounded buses, or are you going to have two ungrounded buses, and the third one is just not used?
The latter is done with heavy duty type panels like Square D's I-Line series whenever it is used for single phase, because the I line doesn't come with anything but three buses for breaker installation, but one big difference between that series and many "miniature" breakers is that you can order breakers specifically designed to connect to A-B, B-C, or A-C for 2 pole units, and you also have to specify which bus a single pole connects to, but you do not have to skip physical mounting spaces.