Not anymore. If you call, there is no option to put a reservation on hold, not even even if you want to call later to redeem. Now you have to ticket it right away. I tried putting an itinerary on hold in April while on the phone, to think about it and call back later (I can never find the lowest level availability using delta.com for my destinations), but the agent said it is not possible, I have to book it or risk loosing it.