I'd also like to point out that unless the OP has been peering over the shoulders of her co-workers, which I imagine would incite remark, she doesn't know what it is they are actually doing. I have on my cell, in addition to the app for the security measure I am required by my job to have, the following:
An app I use exclusively for work that my boss recommended I download as it is more efficient than the website
An app that, while I can use for my personal use, relates to the products my office supports and which app I am expected to be able to demonstrate for our employees
An app which includes, among other things, a map of the campus and the shuttle bus routes/schedules so that I can plan for attendance at off-site meetings
Two apps that, while I downloaded for my personal use, I have found myself using as often for work-related reasons
Additionally, my boss has been known to communicate by text even when we are both in the office.
Whatever you may think of cells in the workplace, workplace culture varies and someone being on their cell phone is not necessarily goofing off.