For some reason it was left out of the Samsung Docs but you need to include the Security Certificates (if upgrading from lower than 4.65) located in the 4.70 zip file and the .pem files located in the root of the zip file. This can only be done via the flash card directly. Copy the whole folder over to the flash card and then reboot the system. Until you do this you will not be able to register a phone to the system, this can be confirmed by turning on the logs in the phone and you will see an error where the phone cannot locate its profile
"Something Something cannot find
https://IP AddressOfSystem/pim/pro/blahblah"
This also goes for any other system that doesn't have the SIP security keys. My 7100 was an older Mp10A and wouldn't work until i copied the folder from the 7400 software package. Also, now that you have created the SIP extensions without the security keys in your 7400 for some reason you cannot use those same spots in the numbering plan unless you default the system. I just used new ports on mine.
As far as how it works it's a fantastic app when on WIFI, when roaming on 4g-3g you need to manually re-register once and a while.