Just to echo everyone else: MAKE THAT CALL NOW!
You almost certainly WON'T be allocated a bulk seat without asking, and certainly not a sky cot (when we flew Continental this summer, we were told 9month-old dd was too old for a cot - apparently they are worried you'll go to sleep and she'll sit up, fall out, do an injury and you'll sue the airline, I expect this is a US airline problem!).
However, more worryingly, YOU MIGHT NOT EVEN BE SEATED ALL TOGETHER! This happened to us (I only called up a week before we flew and it was too late by then as the plane was full). It took a lot of special pleading at the gate to get seats swapped (although it did get sorted). Scarily enough I saw a woman on her own with twins under 2, 2 seats between them, and they hadn't seated them together. The poor woman was panicking.
We bought a 3rd seat for dd (it's not quite as expensive as a full adult seat) which was the best decision and the best £250 I have ever spent. We did get a bulkhead at one point but I actually preffered being in usual seats at the back, close to the toilet, seat arms up, near to the stewards area so it's easy to get rid of food trays etc.
You don't say where you're going but watch out for the not-getting-your-buggy back issue. The worst bit of our holiday was the nearly 2 hours in the queue at immigration in NYC with no buggy. Thank God we'd taken the sling, but even then it was tough with a backpack each, an extra bag and the car seat plus the baby.
Good luck!