Don't know about the other "free ISPs", but FreeServe in UK requires that your telephone's "caller ID" is
not disabled in order to use their service.
I suspect this is to assist in tracking "hacker" type activity as they can go from the IP address used at the time to the login name
and the telephone from where the connection was made!
Issabluudynuisance if you travel though, as you cannot dial into FreeServe from outside UK due to the lack of the caller ID
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What goes around . . .
. . often lands better!