question

We have multiple users in one department that we are giving individual extensions to. They only need one phone because their hours don't overlap much. They will often be using their smartphone apps. We would like them to be able to text when they need to, using the one phone for their office, but that only works for the one extension assigned to the phone. Is there some way we can make all their extensions able to text? We want them to be able to share that single phone.