Airtel gsm service provide 2G and 3G(on reliance 3g network) service in Delhi. I ported one of my number to them to enjoy the really attractive tariff plans. This review is regarding my stay with them
though it was not too long, Thanks to their network and cunning tariff trick.

Network:
Their 2G network atleast in Delhi quite decent though not as robust as Airtel. I do get some blackspots but those were mostly indoors when visiting someone house or few places like old delhi where shops are too walled inside. So better check whether you get good network in Delhi before buying Aircel sim as they use 1800mhz freq which has less penetration than Airtel & Vodafone network in Delhi.
For 3G they roam on Reliance 3G network which usually give me 1-2mbps outdoor.

Tariff plans:
Aircel have many nice rate cutters like business cug pack which gives unlimited calls aircel to aircel & some nice combo pack which gives you min+sms+2g data. However beware their tariff plan page is not updated properly and few plans mentioned have incorrect validity so better ask cust care at 121 before.

What I don’t like:
Your local+std call rate is flat 3p/sec or Rs1.8/min and you can’t change it regardless of their tariff mentioned for any stv used. All STV have mob minutes only but it is not mentioned clearly.
Few 2g data packs like Rs.24 recharge do not carry over your data.
Their 3G recharge are attractive but STV you use won’t be valid if you are on 3G network, even sms pack.

Result:
Its kind of useless to use Aircel in Delhi when you need 3G data and want cheaper tariff plans too specially to landline.
However if you are 2g user only and most of your call are to mobile only then do give them a try.
Recommended if you are a feature phone user and depend more on calls and sms than data.