You would have to ask them how they would prefer to communicate with you, like lipreading as opposed to writing down on papers or would rather sign ASL if they are ASL users. If they are not ASL users, then you have a problem with communicating with them.
As for phone, that is not a good way to do that but if you and the 2 Deaf employees have a smartphone or Blackberry phone which they have use texts in order to communicate. You can do that way.
How about IPad for typing down for communication better than on papers and pens? You just have to find the solution to the communication problem. Being deaf and hard of hearing is not the same like hearing person. There are different degrees of hearing loss from mild to profound deafness.
