featuring a mobile refill service. Through electronic reloading where a specially designed SIM card is used to reload a mobile phone by entering the mobile number and choosing the amount to be loaded. This process is widely implemented in the Philippines and India so that any person can be a prepaid load retailer, creating a nationwide availability of reloading stations, even in remote areas. Credit purchased for a prepaid mobile phone may have a time limit – for example, 120 days from the date the last credit was added. In these cases, customers who do not add more credit before expiration will have their remaining balance depleted through expiration of the credits. There is no compulsion on a prepaid mobile phone user to top up their balance. To maintain revenues, some operators have devised reward schemes designed to encourage frequent top-ups. For example, an operator may offer some free SMS to use next month if a user tops up by a certain amount this month. Unlike postpaid phones, where subscribers have to terminate their contracts, it is not easy for an operator to know when a prepaid subscriber has left the network. To free up resources on the network for new customers, an operator will periodically delete prepaid SIM cards which have not been used for some time, at which point, their service (and its associated phone number) is discontinued. The rules for when this deletion happens vary from operator to operator, but may typically occur after six months to a year of non-use. By 2003, the number of prepaid accounts grew past contract accounts, and by 2007, two-thirds of all mobile phone accounts worldwide were prepaid accounts. History The history of prepaid mobile phones begins in the 1990s, when larger markets were being sought after by the mobile phone operators. Before this date, all mobile phone services were offered on a post-paid basis, which excluded people with poor credit. Prepaid mobile service was invented by Subscriber Computing, Inc., an Orange County company, (1986-1998), founded and directed by Arlene Harris. The patents covering this invention are: US-5291543-A, filed 12/5/1990 and awarded on 9/15/1992. US-5148472-A, filed 6/24/1992 and awarded in 3/1/1994. These patents describe the ability to access the cost of a call and deduct the cost of the call from the user's account balance in near real time. If the user's balance is below the carrier-defined threshold, the next call