Локализуйте Валюту для iPhone

NSNumberFormatter is definitely the way to go! You can set a NSLocale on the NSNumberFormatter, the formatter will automatically behave according to that locale. The default locale for a number formatter is always the currency for the users selected region format.

NSDecimalNumber *someAmount = [NSDecimalNumber decimalNumberWithString:@"5.00"];

NSNumberFormatter *currencyFormatter = [[NSNumberFormatter alloc] init];
[currencyFormatter setNumberStyle:NSNumberFormatterCurrencyStyle];

NSLog(@"%@", [currencyFormatter stringFromNumber:someAmount]);

This will log the amount '5.00' according to the users default region format. If you want to alter the currency you can set:

NSLocale *aLocale = [[NSLocale alloc] initWithLocaleIdentifier: "nl-NL"]
[currencyFormatter setLocale:aLocale];

Which will choose the default currency for that locale.

Often though you're not charging in your user's local currency, but in your own. To force NSNumberFormatter to format in your currency, while keeping the number formatting in the user's preference, use:

currencyFormatter.currencyCode = @"USD"
currencyFormatter.internationalCurrencySymbol = @"$"
currencyFormatter.currencySymbol = @"$"

In en-US this will format as $5.00 in nl-NL it's $ 5,00.