Many graduate students do internships with AT&T over the summer. In 2005, 10 or so went to AT&T at the Florham Park, NJ location.
If you are interested in this type of work, you should look into the collaboration program through the Center for Networked Systems (CNS) or talk to your advisor for other opportunities.
Also see the Intern's Guide for AT&T Florham Park: AT&T/FlorhamPark.