Get Full name from Get-MailBoxPermission

Question

I am trying to build a report with the names of users who have access to shared mailboxes. I have the command running and outputting good information, but it displays a table in the following format:
User
Domain\Username
How can I get output that display's the user's Fullname, first and last? 
Here is the code:
$Users = Get-MailboxPermission -identity callcenter | where {$_.user.tostring() -ne "NT AUTHORITY\SELF" -and $_.IsInherited -eq $false} | Select User
$Users | Format-Table
Thank you for any help

Answer 1

How about this?
$users = Get-MailboxPermission -identity callcenter | where {$_.user -notlike "*NT AUTHORITY\SELF" -and $_.IsInherited -eq $false}
$users | select @{Name="User Name";expression={(Get-Recipient $_.user.tostring()).displayname}} | FT
OR
$users | select @{Name="First Name";expression={(Get-Recipient $_.user.tostring()).FirstName}}, @{Name="Last Name";expression={(Get-Recipient $_.user.tostring()).LastName}}