Usually envelopes do not require Custom forms. Documents have a $0 declared value, therefore do not require tax. If your stealth involves some sort of product that may have a perceived value, then it is always best to declare the correct value of the stealth. So if your sending it inside a cheap Mobile Phone , your declared value would be about $90usd.. Then there may be tax required on it, depending on the destination country. I have had things held up in customs before, because the vendor put a $0 declared value, but the item had a value. Luckily in my instance the custom officers opened it, decided it value is less than the taxable amount and forwarded it on. If the vendor had put a realistic value of hte item, then the item would have just gone straight through customs without a hold up..