a telephone engineer feeds a sound signal into the mouthpiece of a telephone.As part of the tests he is making he incresesthe frequency of the sound.HOW WILL THIS EFFECT TYE ELECTICAL SIGNAL PASSING ALONG THE TELEPHONE WIRE?

It depends. If it is an analoge signal, the frequency. But if it is digital, as on a multiplexed wire, or fiber optics, there will be no difference on the transmitted signal along the "wire".