Portable Wi-Fi hotspot.

This is another valuable reason to buy a Nexus S phone.. ;). The phone should connect to the network first and then can start its hotspot. [Model number : Nexus s, Android version : 2.3.6]. To connect to the network, set the APN  (Access Point Names).

Menu -> Settings -> wireless network -> Mobite networks -> Access Point Names. Press Menu button. New APN.

I used a mobitel (Sri Lanka) sim. So... these are the mobitel settings

Name : Mobitel
APN : mobitel3g
proxy : 192.168.050.163
port : 8080
username :
password :
And keep all others with default values.

Then enable the data access over mobile network.
Menu -> Settings -> Wireless & networks -> Mobile networks -> Data enabled (put a tick)

Now the phone should allow to connect to the internet. [If there are enough signal strength... :)]

Ok... then convert the phone to allow other devices [laptops, phones etc.. which has Wi-Fi] to use the same network connection. In other word make it a "hotspot".

Steps...
Menu -> Settings -> Wireless & networks -> Tethering & portable hotspot -> Portable Wi-Fi hotspot (put a tick)
You can configure Network SSID (Service Set Identifier) and password in hotspot configurations.

Your portable hotspot is ready to use.... ;)