how i interface wavecom modem with 8051???
means is it need max232 or directly?


The modem neither knows nor cares what is connected to its V24 port.
The only requirement is that the connected equipment abides by the signal descriptions provided in the modem’s Manual - it makes no difference whether it’s a PC, a terminal, an 8051, or anything else…

Look at the Manual for the particular modem you have in mind - it tells you what signal levels are used on the various interfaces.

If it says “RS232” then of course you will require an RS232 Transceiver (MAX232 or similar).