I was on the phone with NTT the other day and things were going well (or as good as they could), until I had to spell some email address for the customer rep, and fell upon the letter 'Z'.
Instinctively, I went with 'zed' as a pronunciation, which seemed to stumble the NTT lady, so I tried a 'zee', which did not seem to elicit more comprehension...
Eventually, after trying a few more variations, I had to give up and was told to send that piece of info by email (a rather silly situation, considering I had just been giving and receiving bits of information in Japanese for 15 minutes until that point).
According to Wikipedia, pretty much any pronunciation goes:
Z; Zetto, zeddo, or zī (ゼット, ゼッド, or ズィー, though sometimes pronounced jī, ジー)
It is very possible that, while trying to figure which of the two common native pronunciations to use, I omitted to stress the second mora enough (saying 'zed' instead of a frank 'zeddo' or 'zetto'). But I'm still a bit surprised that she would stumble on this particular instance.
In your experience, is there a more common/natural pronunciation of the letter 'Z' in Japanese? Any circumstances that might dictate the choice of either?