From The Official Star Wars Blog:
"If you still need a good reason to see the new Star Trek movie, this may be it. R2-D2 is in the movie as an Easter Egg, and if you can figure out which scene our beloved astromech makes an appearance, you should enter the “Star Trek Easter Egg Sweepstakes” on Facebook!

Get more info here:
Star Trek Easter Egg Sweepstakes (via Facebook)"

See also:
You Got My Star Wars In Your Star Trek