Check your Friends Mobile Balance
Also Check Out: Some Airtel Secret Codes - Airtel Codes Revealed 2012
UPDATE Well there is an another trick I found fro checking your friends balance in Airtel using Airtel Live Link. So you just have to visit this link http://goo.gl/CdmYvn and then enter your friends Airtel Prepaid Number. That's it it will show you his balance and even his 2G or 3G internet data.
Airtel - well if want to know balance for any Airtel Prepaid Number then you can just dial 09810198101 from your phone no matter which network you have it will work, now after you dial the number just follow below steps.
Select the language.
Then it will ask if you are already using this network press 1.
Now enter your friends mobile number.
Now it will recite that number just press 1 key to confirm that number.
If it asks for any Pin Code just enter 1234
Now it will give you few option just press 1 to choose mobile service.
Now to know the balance and validity of that number just press 1 key.
Now it will recite balance for that number.
Docomo - now if your friend is on Tata Docomo then no matter you can find his mobile balance by just dialing 07737012345 from your phone and then following same steps mentioned above.
Idea - for Idea users you need to dial 09824012345 from your phone and then follow all the steps mentioned above to get the mobile balance.
BSNL - if you friend is on BSNL network then we have a number for that too just dial 9415100123 from your phone and then follow steps mentioned above to get balance for your friends mobile number.
So hopefully this trick will work, well I have checked the Airtel number and its working great, I have not checked other as I do not remember my friends number if they are on which network so they will hopefully work, do comment if you found any problem while using this awesome trick.