it makes a lot of difference - with the online system you are just sending an email request that a real person has to read and respond to. you aren't making a real-time reservation and getting immediate confirmation like you do on the phone. so using the online system may very well put you behind everyone who got up earlier and called FL at 8:59 ET - important if you want an early time stamp for a good view, or if you are trying to make a difficult exchange. so at this point, the phone is the most effective way to get the reservation you want.