Just follow these following simple steps to activate your call conferencing and call waiting.
1. Send an SMS from your mobile: “CLIP NO” to 53738
2. After receiving reply send another sms with the keywords “CLIP YES” to 53738
3. Dial *311 as soon as you receive a reply after sending the second SMS.
Update: 3 way conferencing trick on Reliance prepaid has stopped working and call waiting is now made official.