Airtel recently launched a new Blackberry plan for #1500. It is a month subscription and comes with no data cap, i.e. it is unlimited. It's cheap, works on IOS, android, PC via modem and on other devices.
To subscribe to the plan, load #1500 on your airtel SIM, dial *440*16# and wait till you receive a a confirmation message which confirms the subscription.
For non-BlackBerry devices, the access point should be set as internet.ng.airtel.com