If someone rings me on withheld then I just leave it ring, if it's important they can leave a message....if they have it on withheld it must be for a reason, like they know I don't want to talk to them!
For Christ's sake, if you're my friend and you have a private number, unblock it when you call me. If you ignore my simple request, I'll think you're a telemarketer and either ignore you or pick up and blow my "rape alert" whistle in your ear.
Consider this your first...
they are so annoying i always want to find out who has rung me and find it rude somehow and it makes me feel suspicious but its not as bad as having a heavy breather or long silences on the other end of the phone!