Hinesh, if the phone isn't registered, it could be any number of things. What type of phone is it? Can you please reply with the configuration of the 7100 as well as the config of the phone? For an ADTRAN 7XX phone, the phones are located in the ADTRAN directory after logging in via FTP, formatted as "adtran_macaddress.txt". For Polycom phones, the configs are located in the Polycom directory as "extension-mac.cfg". Thanks
Also verify the phone is plugged into a switchport which is set to trunk port with the voice VLAN allowed, watch the phone as it boots up and ensure it is getting the voice VLAN assigned and getting DHCP in that VLAN. It is possible that DHCP may not be handing out the voice VLAN option during boot and as a result the phone is on the wrong VLAN in this case you may need to hard code the voice VLAN on the phone. As well as the obvious issue of is the phone plugged in the right way and actually receiving power.