Andy Neil wrote:
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"... I suspect that at least some of what you're saying would be dependent upon the particular network that you're connected to?"

It sure does! Here in The Netherlands, the network of KPN (former Dutch PTT) uses DTMF signalling for CLI, which is sent before the first ring. Others, like my cable company, use FSK signalling, but there are at least 3 different methods for that.
Having said that, most devices that support CLI recognition can handle at least those three FSK standards.

Rob.