You've crossed a lot of borders before, haven't you, mixmax? I thought about this proposal of yours for a while as I was eating breakfast, and I remember the wa

You've crossed a lot of borders before, haven't you, mixmax? I thought about this proposal of yours for a while as I was eating breakfast, and I remember the ways that tangible property of travelers can be handled at a border. First of all, if a particular kind of tangible property is declared to be contraband by some country, it can be seized at the border. There is nothing you could do about that, if you want to visit that country, except not bring along the property. Another treatment of some kinds of property is charging a tariff, even if the property will remain in the traveler's possession after leaving the country. I have seen this done. Some items carried by Americans were dutiable in Taiwan even if they were not items that would be sold in Taiwan. (This was in the 1980s.) The customs duty for some items, by the tariff laws Taiwan then had, were equal to the full retail price of the items (mostly consumer electronics, as in the case I observed). Or the property could be held in bonded storage at the airport until you finish your journey. That happens for some items in some countries too. To sum up, just because you can lock your phone doesn't mean you will be able to travel around the world with your phone. Try that in North Korea. Try that in some other places, and see what happens. Countries can control the entry of tangible property into their territory if they so choose.