gauvins

You are right. But the odds of a message not being transmitted are very small (roughly one over 10 000). My personal experience is that unsent messages are rare and easily detected at the source (no clear sky, etc. and you get blinking red lights) so you know that something is wrong. I don't recall reading any account referring to a unit apparently working yet messages not being received.

I don't know whether a duplex network is more likely to process your inbound message. I've used sat phones in the past (in the context of an ocean passage) and would not consider these devices on a bike expedition unless one has very extreme plans and wants to broadcast his/her adventure).

So back to the original question -- I would think that a smartphone tracking app does make sense if you have considered that you'll have to recharge your phone every day if not more than once a day for continuous tracking; and have network access, which is unlikely if you travel in remote areas. A SPOT messenger works essentially everywhere and 2 AAA batteries last several months if the unit is used sparingly or a week if used on a continuous basis.

In my experience, smartphone solutions tend to create unrealistic expectations. If travel plans extend beyond city tours, you may hope to be able to send an update at the end of the day. If you are lucky, you'll have wifi and be able to send your tracks somewhere; or you'll make do with an SMS. Quite frequently, if you travel across less travelled terrains, you'll have to rely on telepathy. Which is underrated.