I have used these devices. Although it was actually part of a module. Since you are from Mumbai following url may be of good,..

RS232 protocol :
http://robosoftsystems.co.in/roboshop/...ation.html

Following are few points to be considered:
1. Data can be sent only at a max rate of 9600.
2. Either bytes, or packets(2-40bytes) at a time is possible, there has to be a gap between two packets (80ms to 280 ms depending on packet size), this normally restricts you from using byte transmission.
3. due to nature of module, they do not appear as a transparent RS232 based rf port but need programming.


Also in mumbai (I have not used this module),

SPI protocol:

http://thinklabs.in/shop/prod...fc179e962f

regards,
Anurag