Interesting thread. Here is my experience. It is technically possible to have foreign ESN in Reliance Network (its no challenge to have a handset programmed to a CDMA network.)
Why Reliance is not doing it? 2 points.
1.) there may be qualcomm royalty involved. which reliance can charge customer for having foreign esn configured on reliance network!
2.) my struggle with reliance support and store people revealed that reliance uses some provisioning database tool which must have the phone esn defined in it. this database at present reconciles esn bought by reliance in this database automatically. I guess there is no provision / process developed by reliance to add additional esn's so far.
With India moving faster than world. not sure how reliance will cope up in having foreign esn's in reliance database when "number portability" across networks will be implemented.
TRAI / DOT may be misled by saying that allowing foreign esn is breach in security. changing esn's and cloning handsets is ..
Good Luck to all.
For "Reliance" people reading this : you are loosing money !!