Hi, all. Need some advice on choosing a mobile provider in India.

I will be spending a couple weeks in DEL, LKO, CCU in a few months. Will carry a tri/quad-band (undecided, maybe Blackberry) GSM phone with me, and I plan to buy a prepaid SIM in India.

Are there any Indian mobile service providers that have nationwide free roaming in north India? Or, if roaming is bound to cost more, any suggestions on service providers that have reasonable pricing and good coverage? If I am forced to choose a "local area", I'll choose Delhi since I usually fly into DEL.
Also on the wish list:
1. If possible, I'd love to get a "lifetime" SIM, so that the phone number wouldn't expire (even if there was no activity on the number for months/years). Is that possible? If there is India-specific jargon/terminology for this stuff, I'll appreciate the education, too :-)
2. If possible, I'd like data/web access included in my prepaid plan, so I can check my email. I do not intend to carry a laptop or netbook, so I cannot use a USB-interface data card.

Thank you, and feel free to move this post to a separate thread if it is not appropriate for the Chai Stall conversation.