Звучит так, как будто вы можете просто удалить пробелы, скобки и переносы.
NSString *phoneNumber = @"(998) 989-8989";
phoneNumber = [phoneNumber stringByReplacingOccurrencesOfString:@"-" withString:@""];
phoneNumber = [phoneNumber stringByReplacingOccurrencesOfString:@"(" withString:@""];
phoneNumber = [phoneNumber stringByReplacingOccurrencesOfString:@")" withString:@""];
phoneNumber = [phoneNumber stringByReplacingOccurrencesOfString:@" " withString:@""];
phoneNumber = [@"tel://" stringByAppendingString:phoneNumber];
[[UIApplication sharedApplication] openURL:phoneNumber];