I just purchased a ticket on line for Marselles to Paris July 21 and it is on a iDTGV train. I thought you could not book past 3 months in advance?
idTGV tickets are available for between 4 and 6 months in advance, depending on the time of year. idTGV trains are TGV trains aimed at young people. There are two "classes" of service, idZen, which bans cell phones, audible audio players....and suggests that passengers with children book in the other class, which is known as idZap. Here you have activities for kids, video games, and the like. No difference in price.