Terminal.getAddresses() will return all the addresses configured on that terminal. There is no easy way to get the Terminal for a particular user unless extension mobility is active on the device. If there is a active EM login session on the phone, getEMLoginUsername() will return the userid. You need to loop through all the terminals to find a match and works if all the users do EM.
AXL API is more appropriate to find the user<->phone configuration.