Just spent several frustrating hours on the phone with CO and UA. For the fourth time since I purchased my ticket for a December flight in April, my flight time and number has changed. First three times it was +/- 30 minutes - no big deal. Today's change was almost 2.5 hours. Fortunately, I was able to negotiate an earlier flight home, so I'm happy. On the other hand, one of my codeshare flights got lost in cyberspace. CO said it was cancelled and UA said it was a go.At this point I wasn't sure who was correct and what was going to happen with my flight. I know they are merging systems etc. but it seems so ridiculous that there is such a disconnect. Finally, after 4 hours of calls, a CO agent was able to solve the problem and confirm all my flights. Unfortunately, my original seating (a family of 4 sitting together "2+2') was lost, so now I'm at the mercy of the online check-in procedure or GA's ,since online seat selection is not available and neither CO or UA can override the system. Any thoughts or suggestions? Please feel free to share.