Among the wireless broadband providers in India, reliance netconnect is currently the best option with wide coverage, good prepaid plans and decent speeds. The modem provided is the Huawei EC 1260 which has native support on Mac OS X (Leopard) and is plug and play. The modem comes with a dialler sotware for mac OS X, which is not needed. However the connection requires to be activated once and this step is best done on a windows computer. (I got it done in the store itself). After activating the modem, plug it into the computer. OS X should mount the modem as a USB device with a manual and dialler software available. You can safely ignore these :)
Open Network Preferences (System Preferences -> Network ). In the network panel there will be one or more Huwaei Mobile devices listed. Only one of these will work and this can be found by trial and error. In the telephone field enter "#777" . Account name and password is your 10 digit reliance netconnect phone number. Press "Apply" to save the configuration. Try connecting. If this is the correct device, it should connect without incident and you will receive an IP address. if it doesn't connect, try the steps above with the other Huwaei devices shown in the panel.
In the advanced tab, you can set your DNS providers. Reliance by default sets it to OpenDNS servers (First time seeing an ISP doing this) but you can add you own if need be.
Reliance advertises the service as "up to 3.1Mbps" but in actual usage the speed widely varies but is mostly below 1 Mbps.