FreeS...can't do any business on the Ham Bands. It's da law.
Zan...we used sailmail everyday in the caribe with only problem being waiting for others to get off frequency. Not really suitable for business needs though as you can't do any attachments and you are limited to 10 minutes a day.
Sounds like you're better off with just plain old SSB and an Iridium for your needs. FWIW...we had both the Icom710 and the M802 and were happy with both though the 802 is really nice. Bill Trayfors really knows his stuff on SSB so you might PM him as you get ready to buy/install for advice.