I am extremly Sorry,The Details are given below.

The first project is, controlling of devices using telephone.
For this project I used AT89C51 uC and a DTMF decoder IC 8870.I have connected a relay with all the precautions.
This unit will answer the call after 4 rings,and from then on if 1 is pressed on the keypad from the other end,relay goes OFF and if 2 is pressed relay is turned ON.

This circuit is working fine.

The other project is also similar,Here I am using only AT89c51 and MAX 232,and a relay.The software is written using VB and has the user interface (Button 1 =ON and Button 2 =OFF).When the user clicks on ON button ,In the microcontroller I check the value and depending on the value I switch the relay ON or OFF.
Even this circuit is working fine.

But when I added the RS 232 interface for the first project,The RS 232 signals are not working.

Is the above info. sufficient,or I need to give some more...

Rgds
Raj