NYBanker,

If by "ultra-compact stroller" you are referring to what I call an "umbrella stroller", then my experience is yes, you should be able to take it on board. (For those FT'ers without children, this type of stroller can be fully collapsed to about the length of a golf umbrella, perhaps 30 inches tall by 4 inches square).

We traveled extensively with DL, Jr. during his stroller days, and usually brought the big Graco which required gate checking, as we would use it when we arrived at our destination. However on a few trips where we didn't expect much stroller use after arrival, we did the umbrella stroller. Flying in F, and with your son in his own seat (and carry-on allowances), you should have no problem. Most FAs, if asked nicely, will allow you to store it in the closet if the overheads are full.

Enjoy this period while it lasts. DL, Jr. was GM before his 1st birthday and was a great traveler before he learned to walk...at which point he wanted nothing to do with sitting on a plane for any length of time. That period lasted about a year until he discovered the joys of being on an airplane (and IFE).