The modem that I bought, is actually an ADSL router from Netgear. Model number is DG834G v3, but as I bought it about 6 months ago, if you buy one now you'll most likely get a future version. It has a wireless port, as well as 4 Ethernet ports. Also Netgear, unlike UT Starcom (the brand of modem that BSNL provided me), has an active website with support, documentation, and firm wire updates. And needless to say, I didn't face any problem from it. It is a hell of a modem. If you don't believe me check out some of the reviews in Google.
Here are the configurations for BSNL Dataone connection. This configurations are mentioned for Netgear, although it should work with any other modem too - only the order and the naming may not exactly match.
1) Basic Settings
Does Internet connection require a login? Yes
Login: [your username without the '@bsnl.in' part]
Password: [your password]
Service name: [you may choose to leave it empty, or optionally put 'bsnl.in' here]
Idle timeout in minutes: 0
Internet IP Address: Get dynamically from ISP
Domain Name Server: Use these DNS - choose any two from the following list of DNS
BSNL DNS: 220.127.116.11, 18.104.22.168, 22.214.171.124, 126.96.36.199
Alternatively, if the above is not working for some problem you can choose Open DNS which is slower, but sometimes more reliable - 188.8.131.52, 184.108.40.206. However it is advisable to switch over to BSNL DNS whenever possible, as it would be much faster for a BSNL connection.
NAT (Network Access Translation): Enabled
2) ADSL Settings
Multiplexing Method: LLC-BASED
DSL Mode: ADSL2+
After these your Internet connection should work. To change any other configuration of the modem, and also for help on the configuration options mentioned above, you can scroll through the Help section that comes in blue on the right side of the page as you adjust the settings.