Shahzad,

There is no problem, if you don't have knowledge. No one on this planet was born with knowledge.

Your first concern is to dial a number on telephone line.

1) The easiest way is to interface a DTMF dialer chip(e.g. MT8880, CMX644) with 8051, and just see if you can produce a DTMF output from that chip.

2) The next step would be to interface your DTMF dialer chip to telephone line. Every chip has different requirement, so it depends what you use for dialling.

3) TEA1062 has a DTMF input pin where you can inject DTMF(or any tone/voice) and it will be transmitted to telephone line. Using TEA1062 has one advantage that it is easily available and very cheap.

4) After you dial a number, you must wait(before you start transmissionof your voice message) until the B-Party goes off-hook.
This is difficult to determine. You will need some call progress detection. Both MT8880 and CMX644 have a call progress detection capability. But its a big pain to implement in software, although possible.

5) When you decide in software that B-party has gone off-hook, then you can transmit your message.

Regards

IA