Are you still getting your phone service from a traditional phone company? Do you have a lot of hard-wired phones that are a pain to switch around? Do your teams need high mobility and have great mobile devices, but still need landlines for long-haul discussions?
Stationary phones aren't going anywhere. For both physical security and comfort reasons, all of the damage that the mobile world could do is already done. Still, landlines can be awkward, especially if you need to drag phone lines, rearrange phone sets, and figure out which numbers go to which outlet and device.