I have your number (Of course not!)

[BobK]

It would depend on the audience. Older people would understand it and recognize it, but the number of people who use it is diminishing (as more and more of us fall off our perch!) .

b

[probus]

Coming back to the idiom itself, if I´ve got that right, you´d say that the average American would understand it.

Hucky

I think so, but in this forum I have learned that there are differences between American and Canadian usage, contrary to what I had always believed. So I'd best leave your question for our American friends to answer.

[Vidor]

AFAIK "I've got his number" is quite common and easily understood in the United States. Although now that I think about it it's probably most commonly used in the third person, he/she has someone's number.

[JMurray]

@Vidor: Although now that I think about it it's probably most commonly used in the third person, he/she has someone's number.

I think this goes for my part of the world too: "It looks like she's got your number" (got you figured out) sounds natural, although slightly dated, ".. got you sussed" is the dominant form.