I have for long been trying to remind people that CLI is an "information" service - it can never be a way of assuredly advising of who is calling. It never gives names, it can only give numbers, so unless the number is recognised it does not tell you who is calling.

There is an absolute right to withhold CLI when it would be presented as the number of the line from which one is calling.

The number of the line from which a call from an outbound call centre is made is of little use anyway. It would never be published or dialled, as it cannot incoming calls. A call centre will therefore present no number at all or a "presentation number". My belief is that a "presentation number" should only be offered to enable continuation or follow up of a call - as telephone numbers are only for the purpose of making a telephone connection. Sadly they are often used to solicit wasted return calls that do nothing more than advise the type of call that was made - which the recipient would know anyway!

It is the duty of every caller to identify themselves to the person who answers their call. If CLI is offered and the number is seen and recognised by the person called, then this can be helpful to them.

Anyone is free to acquire a service that filters calls based on CLI, or assists them in choosing whether or not to answer a call in person. All such approaches however carry a risk of missing important or wanted calls. Most of role played by CLI in the issue of dealing with nuisance calls is mistaken or misrepresented. Its significance is commonly overplayed.

For the case in point, failing to speak when picking up a call is likely to cause a silent call. Many call centres use "Answering Machine Detection" equipment which samples the sound heard when the call is answered in the (commonly mistaken) belief that this will enable a distinction to be made between a live voice and a recorded voice. Only if a "live" voice is heard will the automated dialler transfer the call to an agent.

I have had occasional calls with odd numbers. I think I had one that was "1111111111". As others have said, CLI is readily falsified so it's no problem for a scammer to put anything they like as CLI.

It's also possible for a companay's wrongly configured telephony system to present nonsense CLIs. I've not yet experienced this.

One of my favourite appoaches to unwanted calls is this. When they ask for me by name, I ask in my smoothest professional voice to hold on while I find him. If I'm feeling generous I leave the handset by the radio so they get music on hold.