Thanks so much for the help, ianobi!
With no modifications, the phone connected to my Obi200 shows
UNKNOWN CALLER
15205551456
Using your suggested string, my phone shows "UNKNOWN CALLER" with a blank line below it.
If I change <**1> to just <1>, I get "UNKNOWN CALLER" with a line below it showing the phone number - with an extra 1 prepended to the phone number. (now we're getting somewhere!) That extra 1 at the beginning, however, causes the separating dashes to be omitted.
If I change <1> to <H>, I get "Private Caller" - which, based on what you said, I think probably means that my phone is freaking out over any non-numeric character in the phone number line.
If I try to use <3->, it shows "UNKNOWN CALLER" and the phone number (no dashes) - with a 3 prepended. (The dash appears to be ignored.)
I thought maybe if I used some sort of text delimiter around an alpha character... so I tried <'H'> That gave me the same result as using the default value - "UNKNOWN CALLER" followed by the phone number. Interestingly, it does restore the separating dashes in the phone number: 1-520-555-1466 so basically it's ignoring everything within the "<>"
I got the exact same result when trying to use double quotes instead of single quotes as text delimiters. I also tried back ticks (``) as text delimiters- again, same result.
I'm giving up (for now) on using alpha characters and just trying to get "3" plus a dash or star or space or any sort of separator between it and the phone number that follows. However, it would be really nice to use an alpha prefix as opposed to numeric and I'm wondering... so far, everything I'm doing is only affecting the lower line (where the phone number is displayed) - is there any way to modify the UPPER line (which actually is alphanumeric)?