arfies, The full version firmware you used so your player would accept your dump may not have had the files needed to restore your VOIP function. The only thing I can suggest is there is a full firmware that does support VOIP
HERE. When you load it to the upgrade tool it takes a while (several minutes) for the program to decompress and read the firmware before letting you proceed with the upgrade. If you read the comments on the download it explains this. If it does not fully restore your player then follow it with your dump, but it may contain the files needed to restore VOIP so you do not get the Locked warning.
Let me know how it goes.