I have read the tutorial in twilio but its not quite clear.
Can someone lay down the step by step procedure please?
Here is what I got from twilio:
Exchanging Phone Numbers Between Accounts
You can transfer numbers between subaccounts, and between your master account and any one of your subaccounts. You must use your master account's credentials when making the API request to transfer a phone number.
To transfer a phone number between two accounts that you control, make an HTTP POST request to an IncomingPhoneNumber instance resource URI. In the body of the POST set the parameter 'AccountSid' to the AccountSid of the account you wish to own that number. This will remove the phone number from its original account and make it available under the IncomingPhoneNumbers list resource of the new account while retaining all other properties.
Remember, closing a subaccount as described above will release all of that account's phone numbers, so you might consider transferring all numbers to your master account beforehand if you want to keep them.