After the launch of PCS in 1997, the mobile telephone industry has achieved a remarkable growth in market share and sales, and substituted for long-distance wire communication market. This study investigates the interrelationships between the two markets in transition and attempts to perform the statistical tests if the diffusion of mobile telephone was the direct factor for the reduction in sales of long-distance communication industry. The evidence of the direct substitution effect between the two markets is not likely to be found. Unlike the general expectations, the test result seems to prove the sustained initial complementary relation for awhile.