No , theres no public information on the thread / forum.So only concern is if it's a public thread - you're about to get spammed to kingdom come. Any phone number / email on the internet gets scraped and then called like crazy.
Potentially do it with a private thread (members only), but still somewhat a fear with a spam bot getting on registration. I like the idea of an address book though so maybe something like?
All you would have is a list of members like this…
aaa …. bbb
ccc …. ddd
eee … fff
it would be two members that have swapped lets say mobile numbers.
so if as example …. ddd goes awol or theres something odd on his posts any member can approach ccc to check on ddd to make sure their ok , not hacked etc.
totally voluntary but if it caught on it could help sometimes.
or as you say an address book page somehow?