India

General notes
It is easy to get a prepaid SIM card in India as a foreigner, you just have to make sure you have all the proper documents and they'll probably want photocopies of them too. Documents you'll probably need: The local address proof may or may not be required. Some stores will ask for it, some won't. If you find yourself with a store that insists on it, your only option is to get a local to buy a SIM card for you.
 * Copies of your passport & your passport
 * Passport size photo (probably in color)
 * Copies of your visa & your visa
 * Local government-issued proof of address

IMPORTANT NOTE: You should make sure you specify to whomever you buy the Sim from that you want "international roaming" activated on your device if you intend to leave the state that you purchase the Sim card in. Otherwise as soon as you leave the Indian state you won't have phone service anymore. Also make sure your device is properly configured for the roaming...my Samsung Galaxy S2 had some problems even though I had roaming activated...my Indian friend had to change a few mobile network settings. (24-March-2012)

Dolphin 3G BSNL
Startup Cost: 49 INR, with 12 INR Talk value

Coverage
Big cities only, full 3G speed

Availability
Passport copy and photo required

Prepaid 3G Data Coupons : http://mtnldelhi.in/dolphin/index.php/3g-prepaid-plans

Startup cost
Airtel Sim Card Cost : Rs. 50-100 Rupees, about 1-2 USD, vendors may charge more

Lifetime validity requires a recharge of Rs. 49 which is 1 USD

Data feature packs
3G is easy to get. max at 7.2 mbps network, real world average of 3000kbps. Went to a Kiosk in Mumbai that sold SIM cards with 3G specifically included. I got 2000 MB for 450 Rs, but they had other plans up to 10 GB, I've just forgotten how much they are. You can easily choose when you buy the SIM. 12/2012

Activation takes 2 hours up to 2 days. 3G activation takes up to 4 hours after intial sim card activation.

Technical details
Airtel APN: airtelgprs.com

Startup cost
Sim Card Cost : Rs. 50-100 Rupees, about 1-2 USD, various vendors may charge whatever they feel like Data feature packs 3G is fastest and most reliable in India based on conversations with locals and personal speedtesting.Plans of 2 GB are for 450 Rs, but they had larger and smaller plans up to 10 GB, I've just forgotten how much they are. You can easily choose when you buy the SIM, and have the vendor buy the data pack for you. 12/2012