The previous mention of the online agency being the only one who can make changes is not correct. With flights, and I fly on whichever airline has the best price, I always book via Expedia and have never had problems contacting the airline directly. I generally get check in reminders from both the airline and Expedia. If I want to change seats I do it directly from the airline website. When times have changed I get messages from both and call the airline directly for adjustments as needed.