I paid 4990 with 2000 cash back offer and returned back my SD box to TS. This was a limited time (Saturday) offer they came out with around 3 months back i guess.
Within 2-3 days my account was recharged with 2000 bucks which i used for annual renewal.
We should remember that we own TS+HD STB once we buy it but not the STBs from other providers. If at anytime we shift the provider they would come for repossession of the STB.
Reliance, Airtel and Sun are the providers who either come after non subscribers or repossess only the STBs by repeatedly sending SMSs or calling. There are always exceptions I guess. If one can see the STBs it is clearly mentioned on them that it is the property of the service provider.