Very easy....
Buy "Blank CIM" from any mobile shop for Reliance mobile,
Insert it to you new DUAL CIM Mobile like SPICE 88N or COOLPAD Dual CIM in the CDMA section.
Buy HANDSET TRANSFER CARD from webworld for Rs.25
Follow the procedure give in the HTC card to transfer your number from old mobile to new mobile.
Before you transfer the number, remember to transfer your phone book contacts to R-world using upload facility and after you have tranfered your number to new mobile you can download it back to your new mobile.This way you do not have to manually transfer your contacts to new mobile.
Other way is to use data cable to transfer your phone book to your laptop using OUTLOOK and then in the new mobile copy it back to the mobile from your laptop.