The majority of airlines will allow you to carry-on. If you look on their websites under carry on regulations, there is generally a special circumstances section for things like tennis racquets that could be damaged in the shipping or have strings lose tension and become unplayable.
I have personally carried on my Prince 12 pack back on American, Southwest, Continental, and United. Just make sure you place the bag in the overhead bin correctly with the handles of the racquets in first and they should fit like a glove!
Have fun traveling!
I personally don't trust the airway employees with this substantial investment...