Hi A.,
I have a 3 year old and my husband has been traveling every week (except the Christmas breaks) since October of 2007. He leaves on Sundays and comes back on Friday nights.
We explain everything to our son about the fact that daddy is going to work, flying on an airplane, sleeping in a hotel room...all of it. I think it helps our son to know what daddy is doing.
We also recently bought a webcam and our son LOVES it!
He asks every day to call daddy on the computer phone. It really seems to help.
The other thing we do consistently is call daddy. We talk to him twice a day at about the same time every day...trying to keep everything as much a routine as possible.
Another thing we do is we got a white board calendar so we can mark off the days until daddy gets home. It's helping our son learn the days of the week and it helps him see how as each day passes we get closer to daddy coming home. (I don't know how much of the time aspect he understands, but I know it will help).
Anyway, I hope this helps. It's a big adjustment, but after you have been through it a few times it will get better.
Also, just an FYI, the biggest challenge for us has been bedtime. Since we have two transitions every week, (with daddy coming home and leaving again) the disruption shows up in his willingness to go to bed like a big boy. Its a work in progress! :)
Best wishes and blessings to your family.
R.