Suppose that each of $n$ people knows exactly  one piece of information and all $n$ pieces are  different.  Every time person $A$ phones person $B$, $A$ tells $B$ everything he knows, while tells $A$ nothing. What is the minimum of phone calls between pairs of people needed for everyone to know everything?
1. **Claim**: The minimum number of calls required for everyone to know everything is \(2n - 2\).

2. **Construction**: 
   - Let us designate one person as \(A\).
   - Each of the other \(n-1\) people calls \(A\). After these \(n-1\) calls, \(A\) knows all \(n\) pieces of information.
   - Then, \(A\) calls each of the other \(n-1\) people. After these additional \(n-1\) calls, each of the \(n-1\) people will know all \(n\) pieces of information.
   - Therefore, the total number of calls made is \((n-1) + (n-1) = 2n - 2\).

3. **Bound**:
   - Let \(B\) be the first person to know all \(n\) pieces of information. Suppose this happens at the \(p\)-th call.
   - Before \(B\) knows everything, each of the other \(n-1\) people must have made at least one call to share their information. This accounts for \(n-1\) calls.
   - After \(B\) knows everything, \(B\) must call each of the remaining \(n-1\) people to share the complete information. This accounts for another \(n-1\) calls.
   - Therefore, the total number of calls required is at least \(2(n-1)\).

4. **Verification**:
   - The construction shows that \(2n - 2\) calls are sufficient.
   - The bound shows that at least \(2(n-1)\) calls are necessary.
   - Since \(2(n-1) = 2n - 2\), the construction is optimal.

\[
\boxed{2n - 2}
\]