used Reliance whatsapp plan on GSM, and it was a horrible experience, cause I kept of getting deduction notifications till it was all empty.
Reasons
To keep whatsapp running you would keep phone DATA ON, which will trigger lots of sync
Gmail,calendar, maps,playstore update checks,
android OS update if enabled, so Reliance allowing whatsapp for this cheap price, also gives other apps to run in bag-round and pay them for the usage which you didn't wanted to do.
if you check Whatsapp, excluding images and videos, will consume only a few MB's in a week, but having this plan you would end up paying more than any other data plan available.
If someone wants to use it, make sure you don't have any balance on the phone so other app usage doesn't get thru, however don't know by having a zero balance will this Rs.16 crap would still work.....