3 mos is actually a very easy age for travel--not yet mobile, and generally just eating and sleeping. As long as you feed the infant during takeoff/landing to encourage jaw movement for the ears, should be smooth sailing. The biggest issue for many at that age is they are not yet old enough to have a full set of immunizations, so many (pediatricians) are leery of international travel.

ETA: Just noticed somebody received a year-old thread... not sure why, but answer still applies, although the OP's child is a bit older by now.