I am currently in the process of building a system which allows vehicles to send information back and forth with an Arduino. The main problem I am facing right now, is that the current implementation assumes that a constant internet connection is present, which in certain areas is clearly not the case.
One solution to this problem is resorting to SMS whenever the internet connection fails, but this still also requires a GSM "network" connection to be present.
Are there any other cost-effective means of communication that are widely accessible regardless of the location you are and that do not require either an internet connection or SMS?
TLDR: Are there any cost-effective means of providing global communication of two parties that are not within a close proximity of each other, excluding internet or SMS.