Pros
Ericsson's benefits are great (medical, life insurance, matching 401k, stocks, and many many more), the work/life balance is amazing. If you need a day off, you work it out with your manager and put in for it, they also allow telecommuting when necessary which is a life saver nowadays, especially when you work in IT and don't need to physically be there. The campus was updated when Telcordia was purchased by Ericsson, it is a nice facility, out of what they upgraded, the rest of still old Bellcore from the 80's. If you can get a job with Ericsson, working on Ericsson systems, not one of the (many) companies they have or will be buying out, you're in a GREAT company and should do it. However, if you're joining the former company that was bought out, before or after purchasing by Ericsson, leave while you can on your own terms.
Cons
Since the merger of Ericsson and Telcordia, MOST Telcordia employee's were laid off, and who were not laid off will be at some point. The Piscataway location is a "sunset" location which means they will eventually be shutting it down and want everyone to either move to Plano, TX, Montreal, Canada, elsewhere in the world that they have a presence or you get the boot. Their package for people being laid off isn't bad at all though, so riding it out until then is the best option, however, it doesn't seem as though they're going to be hiring within NJ anytime soon. It's VERY difficult to move around Ericsson and get a different position within the company, without moving around the world anyway. They make it sound easy and that it happens constantly, but it's only true for the unionized EU/Swedish employees.