I've been using the Delorme InReach SE - which is a two-way device that uses the Irridium satellite constallation and has 100% global coverage. You can send and receive 160 character email/text messages you enter on the device (very slow and annoying) or pair it with your iPhone and use a real keyboard (a joy to use). You can post directly to social media too. The unit tells you when your message is delivered, so unlike the spot, you know it got through (or failed to). The Irridium network is great - I have no problem sending/receiving message, even under tree cover. They also include an interactive map for displaying tracking points. There is a new version that includes GPS navigation functions as well, but I haven't tried it...