It's exactly the same as with C variadic functions. That means you can't just pass it through directly, you have to pass a va_list
around. You'll need something like:
+ (NSString *)format:(NSString *)first, ...
{
NSString *string;
va_list args;
va_start(args, first);
string = [[NSString alloc] initWithFormat:first arguments:args];
va_end(args);
return [string autorelease];
}