operator<< overloading

I have two classes that I need to overload the stream operator << on. One works, the other doesn't, but I'm having trouble seeing why the latter doesn't work.

Here they are. I'm hoping someone can help me point out the difference.

/////////////////////////////////////////////////////////////////////////////
// this class overloads << just fine.
class Location {
public:
    Location(Country country, std::string& location_name);
    Country country() const { return myCountry; }
    const std::string& locationName() const { return myLocationName; }
    float longDistanceRateFromCanada() const;

private:
    Country myCountry;
    std::string myLocationName;
};

static std::ostream& operator<<(std::ostream& os, const Location& location) {
    os << location.locationName();
    return os;
}
////////////////////////////////////////////////////////////////
// this class does not

class PhoneNumber {
private:
    unsigned long myPhoneNumber;
public:
    PhoneNumber(unsigned long p) { myPhoneNumber = p; }
    int areaCode();
    unsigned long getNumber();
};

static std::ostream& operator<<(std::ostream& os, const PhoneNumber& pn) {
    os << pn.getNumber();
    return os;
}
///////////////////////////////////////////////////////////

Thanks for any help you can provide.