Share Your Laptop's Internet Connection with Your Phone

                        WiFi Ad Hoc enabler for Android

Most traditionally we use our phone  as modem to connect with laptop/PC to use internet connection.  Generally We use Dial-up type connection mode   to use Internet with phone to Laptop and PC.  But in Some cases we need to connect our phone with Laptop to use Internet  i.e the internet available in Laptop, We want to use it in my phone. 
   This is Known as reverse tethering.   we  can accomplish this "reverse tethering" from our Windows PC or Mac to your Android or iPhone device in a couple of ways.

First Approach 

when you enable/open your wifi on Laptop you are setting up an Ad Hoc network on your laptop. By default, Android wont connect to Ad Hoc networks, so these networks won't show up when you search for new wireless connections.

You have to use Third-party Ad Hoc enablers are available for Android, but they have many known problems and incompatibilities. 

If you want to use this third party AD Hoc Network then you have to  "rooted" your device . 
now what is rooted  Android device ? Android rooting is the process of allowing users of smartphones, tablets, and other devices running the Android mobile operating system to attain privileged control (known as "root access") within Android's subsystem.

Rooting is often performed with the goal of overcoming limitations that carriers and hardware manufacturers put on some devices, resulting in the ability to alter or replace system applications and settings, run specialized apps that require administrator-level permissions, or perform other operations that are otherwise inaccessible to a normal Android user.

After rooting your phone you can use any third party AD Hoc Network app to connect to you Phone(Android Device) with your Laptop. 

For more Detail You can visit this linkhttp://code.google.com/p/android-wifi-tether/http://androidtablethacks.com/android-tablet-hacks/how-to-enable-adhoc-wifi-on-android-tablets/http://www.arenddeboer.com/wifi-ad-hoc-enabler-for-android/

Second Approach
Connectify

Connectify is free software that shares a single Wi-Fi connection over Wi-Fi--no need for a second adapter or for your laptop to be wired to the Internet. It's only available for Windows 7 and above, however. 
One of the main advantages of Connectify over the above methods is that the connection is more secure--using WPA2 encryption in Access Point Mode versus the very insecure WEP, as the ad hoc networking modes above do. 

For detail you can follow this linkhttp://www.connectify.me/hotspot/