Also, when you set up EM, it is set for a specific type of phone, they will only be able to log in to another phone of the same model. ie someone set up for a 7945 will not be able to log in to a 7965 for instance.
FYI:
You can set up multiple EM for the same person using different phone types if you wish, so the log in to any phone is the same for the user, no matter what type of phone they have in front of them. ie one profile for 7945, one for 7965, one for 9971 even, etc. I do not recommend you do this for many people, but as the system administrator/maintainer, you may find this handy to have when trying to troubleshoot possible issues.