OCSG Charging
                     Let us try to understand charging in ocsg by an example sms based application. 
	
	
	
	
                Its a time check application, subscriber (prepaid/postpaid) send an sms with text '?' and application replies with current time. 0.5 usd are charged on 
each time check. If command text is something other than '?', application replies: invalid command, send '?' to check time. Basic ocsg communication services 
used are SmsNotification / ReceiveSms and SendSms, in order of invocation.
Some important features / goals related to charging: 
1- application should not compute current time (business logic), when requesting subscriber is prepaid which do not have enough balance (>= 0.5 usd).
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