My trip next week was booked through Virgin Atlantic and includes fights with Delta. These are between Atlanta and Vegas and vice versa. I went on to the Delta website and chose my seats. I did wonder how much it would be for Delta comfort. It wouldn't let me do it online so I rang Delta on their European number which is a UK number. After a long wait I was told I can't upgrade to Delta Comfort, so I just left it. Last week I checked online and I noticed that the seat numbers on my flights had disappeared. I rank Delta here in the UK and was told they couldn't help. Apparently I was talking to Air France who are one of Delta's partners. The only way I could sort it was ring Delta in the U.S. I rang and got through very quickly (quicker than the UK number.) I spoke to a very nice lady and explained my problem, she assigned me seats on my flights and guess what, she has put me in Delta comfort on both flights for no charge. It seems to me that the number they give for European enquiries is only helpful if you have booked through there partner airlines Air France and KLM..