We got a smart multi line sim to figure out where a person harassing us is getting our number. One number was given to office people and another was given to family and friends. Anyway, we had trouble with the prepaid line. We could not pasa load the account. After 4 visits to a smart wireless center, they were able to figure things out. The multi-line sims cant be switched by, in cases of Nokia phones, pressing the # key for a long time. You have to dial in to a number to switch and dial to another number to check which line is active. Easy enough to program into a phone but a little bit of a hassle as compared to long pressing a key. Still, the trick worked. We localized the leak and in the process of tracing the S.O.B.