Mobile phones are very popular due to small size, low weight, ease of use and increasing improvements in software and hardware. This popularity has caused a significant increase in the application of services via mobile phones since they are almost always available everywhere. One such service is mobile banking. When we talk about banking, financial issues and monetary transactions are discussed and obviously security is an integral part of it. One method is using SMS in mobile banking. In this paper we consider the challenges of using SMS-based mobile banking and finally, by using the parameters of GSM network positioning system we propose a novel protocol for encrypting SMS in mobile banking.