Do not hide number when calling friends?
Possibly.

Your mileage may vary, as this is a carrier dependent function.  I was however able to achieve the following using two AT&amp;T phones in the U.S.

First I opened Settings > Phone > Show my Caller ID and turned the switch off.

Next I placed a test call to the second phone, the other phone correctly displayed "no caller id".   (Note: it does NOT matter who the carrier is for the second phone, all the magic relates to what the first phones carrier offers.)

Next I google "AT&amp;T star codes" and located this list.  *82 looked like the best choice.

I then modified the contact for the second phone, adding *82 before the phone number.

Calling that contact then allowed my caller id info to be displayed on the second phone, while still being blocked for others.

It's my understanding that *82 is reasonably standard for the code itself in the U.S.  I have no idea which carriers support it however (other than AT&amp;T where I did test).  I also have no idea what carriers in other countries might use, or if it's supported with a star code.  Consult Google for "(carrier name) star codes" or check with the carrier.