You can check the status of deployment on US's website:

http://www.usairways.com/en-US/trave...lam_00697&re=1

As it stands right now:

If you're on an A321, you will have it (unless it's broken)
If you're on an A319, you have about a 66% chance of having it on board
If you're on an A320, figure you won't have it and count yourself lucky if you do.

On the Embraer Jets, you'll have it on the E175 and a 50/50 chance on the E170/190.

Until US gets its website updated to show it on their website like they do for the A321's, you're not going to know until you show up for your flight.