Overengineering a solution
"Enum is designed to get around the problem that few phone keypads have an "@" key, which makes dialling an SIP address for a VoIP call tricky. "
Well, yeh, I suppose so. Or you could just use the hash key to stand in for the at sign.
Of course, while massively simpler, infinitely cheaper and vastly more reliable, that does have the disadvantage of not providing a completely spurious excuse to set up a bunch of useless registries as part of a power-grab to try and obtain monopolistic control over the emerging VoIP infrastructure.
Which I suggest is the only possible genuine motive for this otherwise utterly pointless charade.