OMG! This thread is epic

@OP: This is practically impossible nowadays as almost all operators are 'clever' enough to filter out users based on the plans they are subscribed to. If you are not subscribed to a data plan, you will not be able to use PS network (you can use the 'pay as you use' plan). Btw, in some places, you can try recharging for 2G plan and access 3G network. BSNL has some flaws here. However, it is not possible in all circles. If they are using an updated software on the core network nodes, this should have been fixed as I believe user authentication and subscription details are checked at core network level.

EDIT: Btw, GPRS/EDGE plans are dead cheap nowadays Almost all operators give 2GB usage for less than 100 INR p.m (Aircel gives truly unlimited plan for INR 98). Many operators have already come up with affordable 3G plans as well
Eg. BSNL charges 151 INR for 1GB p.m, Aircel charges 198 INR for 1GB (unlimited*) p.m
*After 1GB, speed becomes 128 kbps